What are the easiest AD&D classes to learn for someone only proficient in 5e?

My friend's Dad wants to run a oneshot for his AD&D buddies next week but since they're mainly power gamers he wants to invite some more roleplay proficient players from my 5e group.

That being said, the only thing I know about AD&D is the term THAC0 and that spellcasting works differently. So what's a good class to start with? I don't mind learning a magic class, though would prefer a martial if it's easier.