The best character is always the one you enjoy the look and feel of. The one you enjoy playing.
Conqueror for me. Regardless of how good or bad they are. Don't get me wrong, I'll complain loudly if they're bad but then again I've been in this 'gaming' business long enough to understand if they are too powerful. Where they stand on the power scale is unknown to me but they seem like one of the less popular classes.
If you're just looking to stomp other players with an over powered character or something, then frankly you're looking at the wrong game. Every character, even the ones that might be currently considered "OP" still require a high level of skill to play to their strengths. If you're bad at the game, then you're gonna do poorly regardless of the character you use. If you get good at the game, you'll also do well regardless of character you use. The true scale of a character's power can only really be tested in high level play, which only maybe a few dozen people can call themselves high level players at this point.