im usein mako at the mo an lovein it on my eng/regen...first one is a spirit shark nice knockback an i have just got the hold at 44 pulls fightin targets to the ground...but i will be takein ghost widow on my dark/dark stalker as it will look better
depends what power sets you have but FotM is Black Scorpian
Defiant's GoEH/MILITIS METUS
Black Scorpion's AE immobilise is FotM for brutes in PvP (because it has -fly, -jump, -spd and -rchg on it, so even if you fail to immobilise the target you still inhibit their movement/attacks), but afaik stalkers don't have access to it - iirc they get a snipe, ranged attack, single-target hold and a short-duration pet - iirc Scirocco offers the same, and Ghost Widow definitely does (I'm going with her for concept reasons, but none of the patron powers fill me with excitement).
Mako offers a Tornado-type Water Spout attack instead of a snipe, which I've variously heard is either rubbish or the best thing ever, but that was re PvE. You'd have to ask another PvP-ing stalker who'd taken Mako what it's like - I've only bumped into one 41+ person on Union so far who has taken Mako, and he was a stalker with the Water Spout (he summoned it by the arbiter in Grandville), but I can't recall his name 
Stalkers get some of the best out of the PPP. I like ghost widow the best because you get the night widow, which can piss your enemy off.
OK if you dont know me im very into PvP, My stalkers fast approching lvl 40 so epic power choice looms.
Anyone have any good ideas which is best for pvp ?