As Lemon said, HUcast has the highest ATP in the game. But, at the same time, it has the lowest ATA of the four Hunters. I personally the strongest end-game classes are FOmarl, HUcaseal, RAcast, FOnewearl, HUcast, and RAmar.
I'm just gonna make a list of END-GAME gear here: Psycho Raven set, 85-hit Crimson Sword, Dark Flow set, S-Rank Handgun (zalure), S-Rank J-Cutter (arrest, hell, zalure), TypeME/Mechguns (demon), Slicer of Vengeance, Ultima Reaper set (or just 1 with 80 hit), Asteron Striker, Diska of Braveman set, Suppressed Gun (charge, arrest), Inferno Girasole set, Lavis Blade (for DF health only), Hundred Souls or Excalibur set, S-Red's Blades, Jizai set, and a whole bunch of other stuff. There are LOADS of weapons that are good for Hunter. If you'd like, PM me and I'll add a few more this list
The class that "levels" the fastest is Force (in my opinion), because they have the ability to tag/debuff pretty much everything and hardly ever miss out on getting exp. The fastest way to level, though, is to do CCA (especially with x5 on). In my experience, people are always willing to help unlock it on Ultimate
Soly already answered this