This will obviously change, but here's how i understand our current state:
SV: Last in single target, last in aoe. A holy priest could output similar levels of dps.
BM: Will probably be the highest dps until mythic gear (665 gear shows BM ahead of Marks), where MM will start outscaling it. Plays pretty much the same as live. Stat prio (single target): MS>Crit/mastery>versatility>haste. MS (mutlistrike) will affect both the hunter and pet, however, it currently doesn't proc off beast cleave, making it useless of AOE.
MM: Weapon scaling is insane for marks (10.99 vs 5.61 for BM). I hope this doesn't get nerfed though, as hunters have historically scaled poorly. My guess is once you get a mythic weapon, combined with the 4pc bonus, marks will outscale BM. The spec is noticeably different then live:
1. Mastery has been changed, you now get a buff after standing still for three seconds (it last for 6 seconds if you move afterwards). You trade the mobility we're used to for sweet, sweet damage.
2. Chimera shot can hit two targets, which addresses our lack of cleave.
3. Rapid Fire will give you the careful aim buff (increased crit on aimed shot)
Barrage vs GT vs PS
Barrage is the highest dps, though it now has a 20s cd at 60 focus, so it felt clunky to use.