I think T-90 is pretty much all EC's use now. I'd be hardpressed in my area to find a supplier that carries RW90 in anything under #3 AWG. There is two types of T90 though...One being approved for wet locations (THWN) and resistant to sunlight and one that is not (THHN). If you're pulling anything over 1/0 underground RW90 is going to be a B!TCH to pull without a ton of 77 in the pipe! I've pulled THWN in for services before and have never had a problem so far...
-CJ
