If you want something simple to learn the rules on, fighter, rogue, or barbarian would be my go-to. Anything spellcaster-related is going to have a lot of homework to learn all the spells and the most strategically efficient ways to use them.
@FaeLuna the mage used to be my favorite for the original game. I guess if that world actually existed I'd be a mix between a mage and fighter. A hybrid.
@Encontrados I mean, multiclassing is a thing you can do. I wouldn't recommend it for a first time player, though, because that gets even more complicated than one class.