Personally, I'd go Proto. Decent float in powder, blunted tips mean you can downsize without giving up effective edge length, and similar flex profile to the SL - not too stiff to play and not too soft to bomb.
The Cobra doesn't make much sense for you if the majority of your riding is on the east coast. It's basically a playful powder stick. Sucks for riding switch and I found it to be twitchy on groomers.
The Heritage is a great board, but again, for primarily east coast riding, I think it's just too much stick.
The SL is a great all-around board, but I prefer the blunted tips of the Proto. IMHO, the Proto pretty much made the SL all but obsolete.
If you really want a great powder performer, you can always demo a true pow stick when you go out west if you get lucky and get a truly deep powder day.
What size would you suggest for me? The store that I contacted only had a 154. I was thinking a 152 would be better for my size.