Personally, I use Mate. But if I was starting out, I wouldn't worry so much about the differences between the frameworks. I would flip a coin and go with one, (RobotLegs cause it has a cooler name). The biggest hurdle is generally, getting yourself to think about programming with architectural considerations. Once the singletons and autonomous views go away, you are faced with a whole new outlook on programming which can seem like a never ending journey.
Im using robot lets rite now, there are lot more classes/files than what cairngorm uses, it completelyyyyyyyyy separates all the layers... if a UI guy is working on UI, he need not worry about data/services etc., very useful ! I worked on Mate as well, does not support pure injection, have to use a lot of singletons to get it to work, ths is also a good framework. I'm not aware of swiz.
I'd personally choose Parsley. But you might want to check out Piotr Walczyszyn's AS microarchiteture video on Adobe TV
In it he compares all of the current crop of microarchitectures and incorporates the PM pattern from Cairngorm 3.