FWIW we’re using Jersey as its packed full of features (e.g. WADL, implicit views, XML/JSON/Atom support) has a large and vibrant developer community behind it and has great spring integration.
If you use JBoss/SEAM you might find RESTeasy integrates a little better – but if you use Spring for Dependency Injection then Jersey seems the easiest, most popular, active and functional implementation.