i'd go 11-26, especially with a compact crank. i've been using shimano 11-25 cassettes but it's basically the same. 50x11 is a bigger gear than 53x12 and will almost always give you enough top-end speed, and 34x25 or 26 should be enough to get you up just about any hill. i've used both of those extreme gears in multiple rides and races but almost never felt like i needed a wider range (with the exception of a certain stage race over the summer when i used an 11-28 and still barely made it up the hill).