I'm a Specialized fan myself, with a 2009 Sirrus just purchased tuesday. I would say go with the ariel, if you dont mind the WIDE tires it has. Ive seen the crosstrail in person, which as you know is the mens version, and the tires are pretty wide for dedicated street use. Since you mentioned riding mostly trails and around town, Sounds perfect. If you need to hop curbs, you WILL appreciate wider tires and suspension fork
Same with ruts and stuff on bike paths.
The trek FX line are good bikes, but will be a bit rougher over bumps. Unless you only have smooth bike paths and streets with no potholes
also, It looks like Specialized made the geometry of the Ariel a little more upright than the crosstrail, something you might like or might not. Definitely go to a bike shop and test ride a few models, see what fits your style the best!