DM: Chancellor Neighsay dispels the magical chains…
Gallus (RD): Okay rush him go go go!
DM: If you'd let me finish my sentence, you would have heard "…just as Sandbar closes the locked door."
Gallus (RD): …Unless he leaves it open!
Sandbar (AJ): Nah.
Gallus (RD): Then I'll pick the lock!
DM: It seems Neighsay has cast Arcane Locks upon the door and window.
Gallus (RD): Yona could try smashing them! Or any of the others could do something magical!
DM: <sigh> I can see it would be counterproductive to stop you outright, but I must insist you take at least a short rest to get back up from zero.
Sandbar (AJ): Where do the Chancellor and I go afterwards?
DM: Neighsay leaves you to your own devices. He returns to the Headmare's office to start planning his big changes for the school.
Sandbar (AJ): What about Cozy Glow?
DM: She went elsewhere while he was carrying you all to the dorms. You have no idea where she's gone.
Sandbar (AJ): Hmmm. I have some idea… But I might need backup. The School of Friendship is located in Ponyville, right? Is Sweet Apple Acres still around?
DM: …It's always about connections with you, isn't it?
If there's one thing I've learned over the years, it's that if your player is dead-set on doing some kind of Risky but Cool Thing... it's probably best for the experience overall if you find some way to let them do that, even accomplish some minor victory with it.
There's many caveats to that philosophy, of course, not the least of which being if the Risky but Cool Thing is also a Really, Really Stupid Thing.
My old group used to do a lot of NWoD games. Mortal, Changling, Vampire x2. Each campaign would take place in the same time, Waco, TX, and the events would be after the other. There were a couple times past parties would be mentioned, but there was one time my Changling character, who was a computer hacker (by being a computer), had to help our 2nd Vampire group.
My current pathfinder party has that as a rather valid argument for being doable. One of our players, currently a paladin, was the paladin's sister (a gunslinger) the past go round; while the events of the past go round are no longer valid as they and myself are the only players from that group reprising the campaign romp, as their characters are siblings, it only makes sense for them to talk.
As to "talking with higher powered past-campaign you in a campaign taking place afterwards" style of your question, I got nothing.
Every Shadowrun game a friend of mine runs is set in the same "world" and most if not all of the old characters are still around somewhere. One old gang that started out as "level 0" teens went legit and became a peacekeeping force; they're now the de facto cops of sorts in the area the current game takes place in, and the old PCs are now the board of directors.
I've had characters occasionally reference each other/have history with each other. Though in some cases those campaigns were actually running simultaneously instead of as sequels.
My current Pathfinder character is explicitly my last go-around's mentee.
As I ALSO helped flesh out this world with the DM, I get Insight rolls for knowledge that my younger character should know from growing up with one of the saviors of the world LITERALLY dandling her on her knee.
I always say start with a rogue. They're fairly simple, have several viable builds or flavors, and give new players a lot of options for how they play their first few games. Rogues also teach some of the particulars of combat and teach the importance of positioning early on. The high number of available skills make it easy for rogue players to feel valuable to the game and offer lots of opportunities to taste some early success.
My first experience as a rogue didn't work that good. Maybe it could, if I didn't try to make "social rogue," and the DM wasn't so much in love with monsters immune to backstab.
Fighter, hands down. No special powers/abilities, no rage, no extra die. It's the perfect class to get someone completely new into a game and introduced to mechanics. Once they get that down after a few sessions, you can upgrade them to Barbarian or Rogue.
Once they wish to try their hand at magic, Sorcerer would be easier than any other magic class, maybe Bard, and Warlock for 5th edition. Cleric, Wizard, and Druid no matter the edition should be avoided unless they really like the bookkeeping and organization that comes with them.
The obvious answer but this is the class that least gets in the way of learning how to 5e (I admit, I am presuming 5e from the above comic, but I'm running with it) largely because you have so few decisions you have to make. And your decisions (mostly your Martial Styles) have are small enough effect that a 'wrong' choice won't severely hinder the party (and most DMs I know will let you retcon a martial style that turns out not to be your character's thing.
The Fighter is also probably the best class to explore things besides 'make the monster stop living with my sword' actions in combat (Grappling, Shove, etc) if only because if you do the wrong thing at the wrong time you have the armor and HP to (probably) survive it.
You will also have to learn to stay on top of your passive buffs "Excuse me DM, but that 19 is a crit because I am a Champion.", which is something most people I run with could use more practice with.
Huh. My title didn't get posted. Ah well, it was Fighter (Martial Champion). Probably obvious, but I don't think it's until the second paragraph that I otherwise named the actual class.
Good tutorial character? Literally anything the new player wants to play.
Keep in mind that I started out with D&D 4e, where all of the classes had about the same level of complexity; Fighters had just as many options as Wizards, so it didn't make much of a difference what you started out playing.
But that having been said, I think the best way to learn the game is to jump right in and learn as many rules as you're comfortable with; new players shouldn't be shackled to the "easy" classes if they don't want to do that. The only real concern is whether or not the player has access to a Handbook. If they have the book, and enough time to read it, then what's stopping them from rolling a Wizard right out of the gate?
To answer, it really depends on the player who you are introducing.
If its someone who likes choice, and how choice really matters. Wizard.
Is it someone that prefers to try and be the multi-faceted one? Rogue.
Someone that mixes both perhaps, or has a get in and out deal. Arcane trickster or Eldritch knight.
Really, the player you are introducing likely has ways or ideas on what works for them in how they approach things.
By working with, you may get lucky and find that immediate 'class' that fits them. Or you may not, but you also help them see the work that classes like that are, for later use if the first doesnt fit. But in listening to them, they find something happy wise, and you can earn good points in helping be the good gm for listening and for trying to work with them.
See... back in my first ever D&D group, we had this player. He was insistent on preventing me from railroading. Okay, fine, no big deal, right? So, they get to this giant city where they are supposed to get into the castle and fight an evil dragon that has taken over it. The player spends the entire session trying to find ways to avoid going to the castle, and instead some way of defeating the boss without ever going there.
One example was, he wanted to just blow up the castle using a cannon. I had to tell him there was no way he could do that because he was a 4 inch tall pixie. No matter what kind of Strength roll he made, there's no way he could move a cannon, and even if he could, did he think a city full of people wouldn't notice him moving one? I was surprised when he literally got so angry at me he actually stormed out and refused to play anymore.
Like, yes, I'm all for not being railroaded, and sometimes as the DM you have to let them do a thing. But other times... it literally just makes no sense for them to even come up with such a plan (I should note that said pixie had, up until that moment, been a bloodthirsty, charge-at-all-enemies-without-thought type character, so for said character to suddenly become a tactician made no sense) and you have to put your foot down. It's also surprising just how much that can ruin someone's interest in the game...
I say all of this, and then it reminds me that the same player once ran a D&D campaign where he threw a player in a prison and then kept coming up with reasons why they couldn't get out of the prison if it didn't match up with the way he wanted them to get out... Eh... anyway... this was supposed to be a fun story and I guess became more of a rant instead?
Doing the "risky but cool" thing? I've been "lucky" enough to have effectively one regular in my campaign at work, and right now the kid is dead-set on raising a pet monster. Specifically a salamander. (It's basically a Warhammer salamander, a dinosaur-style lizard, but still.)
The occasional but regular sessions where only he shows up are good for him trying to train or find a home for the lizard.
So far he's been attacked by harpies while trying to hatch the eggs in a hot spring, taken over (and set afire) the base bath-house, and tried, unsuccessfully, to train the increasingly intelligent monster to hunt squirrels on command (it set the forest on fire instead, angering the local woodcutters).
I think having connections is a VERY important thing in RPGs. The sad fact is that you can't always depend on your fellow PCs all the time, so when you need help with info or a confrontation, or even acquiring specific gear, you gotta have NPCs that you can reach out to. Networking is very important for the aspiring hero!
There's many caveats to that philosophy, of course, not the least of which being if the Risky but Cool Thing is also a Really, Really Stupid Thing.