So, the big buffs:
Generals - These guys technically didn't get buffed, but rather the cav nerfs brought things back to their level. The difference in movement between a general and a paladin is now just 2 spaces instead of 4, which makes a massive difference. The fact that generals can get sigurd and canter also hugely helps their move penalties. Then, you factor in their "unbreakable" nature, which is a new mechanic buff for them.
Warriors and Bersekers - As others have mentioned, these guys are back full force. All of the benefits from the gba games are here, plus more, making them really strong.
The nerfs:
Paladins - Max movement of 6 is a huge drop off, plus canter now being assigned to every class really drops cav utility in general. It's not so bad for great knights, but paladins really feel it.
Wyvern Knights - Same thing as paladins, but more. No more free dismounts to offset their weaknesses, 6 movement, etc. But fliers in general are made even worse by the fact that most map design doesn't really give them a lot of benefit from their flying nature. Maps like Ch14, for example, are littered with terrain that's flier impassible anyway. Wind and archers are now far more common as well, so even though the class isn't that bad in general, they have a lot less utility in the game.