I’m personally torn between the Magic User and the Thief. It’s not that I don’t like the Fighter, but I think he’s a bit… boring? He’s very strong, he solves problems by force and while there’s nothing wrong with that, it lacks a bit of cunning I personally prefer.
Choosing the Thief gives you a lock pick at the beginning of the game, which can be quite useful. The Magic User starts with the Zap spell, which is… not that great a spell to be honest 😀
So for QfG I would probably prefer a Thief with magic abilities over a Magic User with thieving skills. But during later games in the series, you can get some special spells if you are a Magic User, so if you want to play the entire series with the same character, picking this class might be interesting.
And if you’re a magic user (or have magic abilities) it’s highly advisable to invest in some spells early on. They are your main way to solve problems. Without them you might as well be a filthy non-magic user! 😀
Another thing I just remembered that really helps: draw a map of the world as you explore it! It’s really useful later on to be able to travel in an efficient way. It’s also useful to know where to go when you’re in danger and need a safe spot to come to your senses.
And let’s be honest, it’s also loads of fun to draw maps on paper 😀