I live in the PNW and I would say that there are a lot of factors in play. If you plan on training in open water before mid June, I would recommend a full sleeved suit. If you're only going to open water in late June through the end of the season, you could get a sleeveless. That's what I wear. But I bought mine many years ago when the technology wasn't as good and having sleeves meant giving up flexibility. So I put up with being cold a lot of the time. Now the quality of the neoprene is better and having sleeves doesn't limit reach. There is the increased cost with a sleeved suit and the clausterphobia factor that someone else mentioned.

I will second looking into Promotion. they have very good prices, the suit quality is excellent. And if you really can't decide, they have a sleevless that will take a long sleeved top. It would work well for training in the colder temps but I don't think that I would race in it.

http://www.wetsuit.com/

Their shop is here in the Gorge and I am familiar with the owners and a lot of athletes that use their suits. It's not a tough trip from Seattle if you want to come down here and check it out.