what is the best class in dungeons and dragons?
I agree with the "one you like to play".
But a fun question might be, which is the most "powerful" and least powerful. Basically a question of balance.
5e looks to be very balanced for the most part. The big issue is that if your rest rate is significantly more often than the expected, those with daily (long-rest) powers will be over powered compared to their non-rest or short-rest peers. So casters will be OP in a lot of "outdoor exploration" games (one encounter per day isn't uncommon IME).
As far as my favorite, I think I'm leaning toward fighter or warlock.
Good answer, Sacrosanct. I was going to toss out a counter question; what dice color is the best to use for D&D? I supposed if that one ever gets definitively answered, we'll be able to do the same for what class is "best".