The coleman is easily the most accessible. Yep, it's farther. But there is so much more area to practice and a much easier approach than any of the Rainier locations. Yeah, the lower Nisqually, but honestly, I think it will take you longer to get to that than to just bite the bullet and go to the coleman. On the other hand, I've found the best training for yearly ice is - HARD CLIMBING IN THE GYM and FAUX MIXED CLIMBING with THESE: http://www.dryicetools.com/
I've been climbing ice hard for 5 years and have been prepared for each season by hard training in the climbing gym mostly - and some cardio for approaches. I usually bug out of town and head to Bozeman or Ouray but I've also climbed a bit at Alpental and Banks Lake. I'd love to get up to Canmore, but I just haven't found the time or vacation.
Coleman is great because you can swing tools, find great short pitches, toprope and even put up a few contrived multipitch lines - I love practicing there. The best part is that there is enough solid serac areas that you don't have to climb inside a crevasse - you can put a strong day of training together WITHOUT lowering and climbing out.
Good luck!
(And let me know if you need a set of technical ice crampons, I'm going to be putting up some Rambo 4 crampons for sale).