Mungs,
Your choice (if any) depends on a number of factors:
1. TSA clearance for training (Alien Flight Student Program -
www.flightschoolcandidates.gov). Your work visa may not allow flight training. You'll have to speak to someone at the school(s) for detailed info.
2. Which flavour of helicopter? I think NEHA uses S300s, and East coast Aero uses R22/R44. If you're flush with cash take a flight in the EC120 with Helicopter Services Boston (
www.bostonhelicopter.com), although they don't do primary training in this, but will probably point you to East Coast and their R44.
3. Getting to the training location. East Coast Aero I think is accessible via public transport, but it involves subway & bus I think. Not sure about Plymouth, but in any case a car is your best bet.
4. Further afield there's CR Helicopters in Nashua, NH. Definitely a car ride away.
Hope this helps and good luck.