I've got Shimano BR-R550s and Tektro CR720s on two bikes. They both work well, particularly after installing KoolStop pads. My mechanics apparently did a great job setting them up because they stop better than the Ultegra caliper brakes (also w/ Koolstops) on my other bikes. They don't squeal unless the rims or pads are dirty and stop much better in the rain than caliper brakes. Both brakes work equally well but I prefer the Shimanos to the Tektros because they don't jut out so much on the sides. They Shimanos also seem like they would hold up better over time.