I did all my ratings at Bristow's Academy and they did me proud. I was in Titusville FL and didn't have any major problems with weather, a few cancellations due to thunderstorms between June and August but the rest of the time it was great. With 40+ helicopters on the line there's rarely any aircraft availability issues too, unlike many schools. Another US school I have personal knowledge of that I'd highly recommend is Rotors of the Rockies in Denver CO but unfortunately they don't issue J1 visas.
I'd recommend dropping an email to Sam at Bristow's Academy - her contact details are on their website at
www.heli.com
The J1 visa is definitely the one to go for - it gives you 2 years in the USA to get trained up then do some CFI work to build flight time. Some CFIs can get the magic 1000 in that time, but it's hard work.
Good luck!
Kris