They all offer airport shuttles and a free breakfast for platinum guests. You can walk to the metro from the Marriotts but need to catch a shuttle from the Ren. The price is the same for my timeframe. I seem to remember that I stayed at the Crystal city before and it was acceptable but not the others.
I have stayed at both and prefer the Crystal Gateway. Thought the Crystal City was a bit dated and did not like how the elevator goes from the shops area directly to hotel floors. The Crystal Gateway you walk through the lobby, which was also much nicer, to get to the elevators. Both are accessible from the Crystal City Metro station without having to go outside, very nice in inclement weather. You just walk through the shop area. It is a bit circuitous, but just follow the signs. Never stayed at the Renaissance.