With the change in PvP level-range restrictions, endgame is surely the most popular. As for the best character, it's pretty unknown right now (mostly because a lot of people are still leveling). I'd recommend asking some lv. 100's about their PvP experiences to get an idea. I suspect that down the road when STS is feeling a new update and more people have tested out the PvP, there will be tweaks and other adjustments to the stats/gear.