When we play AD&D next:
Low vs. High Level
I think low-level play and high-level play are equally unforgiving in some respects. Low-level because a single mistake can cost your irreplaceable resources or kill your character. High-level because you have more resources but if you aren't clever about how to use them - or experienced in what's actually needed and what isn't - the higher-level threats can end you or cost you resources you need to solve a problem.
Mid Level Sweet Spot?
For people new to AD&D, mid-levels seem to be okay. You have enough HP and spells to get some stuff done but also not to die in a single good roll by the DM.
Very High Level is Tricky
Unless you scale down the opposition, very high level play is tough. When we played GURPS Dungeon Fantasy for the first time, it helped that we had PCs who badly outmatched the other side. That way while the players were learning what the power level played like, they had wiggle room on inefficient tactics and on weaker foes. In AD&D, if I toss level 14+ characters at my players and then expect them to deal with level-appropriate challenges, that's asking a lot. They just aren't as familiar with the play of the game. We witnessed that in White Plume Mountain, too, where resources were occasionally frittered away, it was hard to get used to HP as something you couldn't heal back up with rest and time in the dungeon, and then resources were husbanded when they could have been most efficiently expended.
So I think of the three, mid-level is the most forgiving for relative newbies.
All of that said, if the players vote on, say, G1-3, we'll play at the appropriate level (which just might be the pregens, although they're a bit high-powered for G1 in my experience.) Tomb of Horrors will use the list of PCs in the back. C2 might be the best choice, but it may not be chosen. And that's okay. These are only paper men, making real memories.