I think in terms of appearance, the Nightstalker looks most awesome. Something about that bow he zaps up. In terms of benefit, I think Sunbreaker has the potential to empower the Titan class the most. I mena, a continuous, long-range Super, like Arc Blade? YES PLEEZ!

From the footage of the classes so far... I think the new warlock subclass will be a squishy pve AOE class(seemed to take a lot of damage in their chained super in crucible play) Hunters will have a very big role to play in raids and pvp with their subclass. In the right hands nightstalker will be lethal against a team... You just have to find one willing to be a team player. School is about to start though... Titans should be good with their new subclass, but only because they are being given a tool the warlocks and hunters have had the entire time...range.