The Come For The Ride blog evaluates FourSquare vs Gowalla and picks a winner at:
http://comefortheride.com/foursquare-vs-gowalla-sxswi-2010-we-have-a-win...

Here's the post:

FourSquare vs. Gowalla at SXSWi 2010: We Have a Winner!
3.18.2010

I’ve been using the iPhone version of both FourSquare and Gowalla for months now and have thoroughly enjoyed both apps. As similar as they are, FourSquare does a better job as my social compass while Gowalla serves as my digital passport.