Does this have a loose fit or an athletic fit? How would the fit compare to an Arc'teryx Alpha SV or Beta AR (newer Beta is about the same size as the Alpha).

I'm 6 ft and 174 lbs and find the XL to be the perfect size. It's a little loose to allow for underlayering, but doesn't look baggy even with a t-shirt. Sleeve size is perfect. Don't think i'd want a L. That would be a pretty trim fit, but honestly haven't tried one.

I`d say Rab are an athletic, slim fit. If you`re neither overweight nor anorexic, Rab will fit you

A loose fit if you size it right. I'm 6'-0" and about 190 and I wear a large over my Arcteryx Gamma SV softshell and a Capilene 3 base most of the time. If I was was inclined to need more layers, I would want an XL or the Alpha. If you primarily need rain gear, save few bucks and go with the Latok Alpine, although it will also do nicely for winter use under most conditions, but w/o pit zips and not quite as burly. Not by any means an athletic fit, but it is cut closer than my Alpha SV. Of the two, I definitely use the Rab the most. eVent is superb! Very user friendly brim and hood adjustment. Fantastic piece. Also have a look at the Westcomb Mirage (Swamp!).