Cobra Strike. Yeah its good. I dont have it on my MA/Regen cause Im darkness mastery (concept), which gives me a ranged hold. You dont want this solution, you want focussed accuracy for PvP, which will leave you without somekind of 100% stun/hold unless you take it. I would get it.
2 acc 2 stuns 2 recharge.
Cripling. Get for damage. Its the 3rd hardest hitting attack, you can get.
The -fly is 100% certain, granted that you hit. The immobs doesnt win battles, when everyone has combat jump (protection from immob).
Lvl35 is fine. IH is overrated IMO. The heals can keep you alive in both PvE and PvP.
A Paragon Defender
Cheers for the info 
. It means i dont have to take air superiority to stop those pesky villains flying away. Ill probably get Cobra Strike a bit later on and the same with IH.
IH is that hot.
World of Jackcraft.
Crippling axe kick may be ok damage, but the animation time is just SO long, which makes it unpopular for many MA scrappers. I personally don't use it. I have seen others use it however, so It's all down to personal preference.
If youre intrested in the -fly element I would reccomend taking air supiority instead of CaK because as mentioned before the animation time is too long. I personally love having IH in Sirens gotten me out of many situations in the past even one time when it was 4 on 1 activated IH and took down 3 before the last one ran away 
but I can see why you would take IH later as recon and dull pain are often enough
thePhilosopher Martial Arts/Regen/Fire Scrapper
theRegulator Empathy/Energy/Soul Defender
Total Inertia Ice Blast/Kinetics/Psy Corruptor
Total Inferno Ice Blast/Thermal/Leviathan Corruptor
This post is just to try and answer some of questions about the ma and regen powers and how good they really are in pvp. Ive got a 26 ma/regen scrapper and I love him to bits at the moment but hes given me a few things to think over. Im trying 2 cram as many good powers into the first 30 lvls for sirens call but Im not sure which are any good for pvp or not.
Cobra strike: I was just wondering if it disorients every time and is it worth taking when you come across dominators and the like with no mez protection. Or whether I can live without it since I dont think many other scrapper sets have a disorient power.
Crippling axe kick: I know the immobilise part of this power only works 50% of the time in pvp iirc but what about the fly element.
Instant healing: I know its a must for the later lvls coming up against elite bosses but in pvp is it that hot. Im planning on 6 slotting dull pain and reconstruction 3 rchg 3 heal and ive got hasten. Taking this into consideration I wasnt planning on taking it till 35 due to its long down time and rely on the heals.