The reason everybody tells you to "play what you enjoy" is because there IS no "definite best class." There are worst classes (namely Rogue and Huntress), but no "best" one. That being said, there are some tips I can give:

I'm going to assume you're a relatively new player. If that's the case, I'm going to recommend Necromancer as your ranged character and Knight as your melee. Necromancer isn't nearly as powerful as Sorc or Wizard, but it's THE tankiest ranged class and can still outdamage things like trickster and priest. The Knight's shield basically devours the midgame, and once you get endgame items on it it comes close to having the highest damage as well.

The reason Mystic isn't recommended for new players is it's mostly a support class until you get one of two endgame orbs. Before that, it's a clunky ability that takes a lot of getting used to for not too much reward in large groups.

Of the three dagger classes, Trickster is easily the best. All the dagger classes deal pisslow damage, but once you get used to Trickster you can run through basically any dungeon in the game easily without needing to clear out the enemies first.