I've used both types on our tandem, and prefer the bar-ends for these reasons. #1 is the visual and tactile indication of what gear I am in. I can feel what gear I am in without taking my eys off the road. STI levers look and feel the same no matter which gear you are in. #2 is the lack of front derailer indexing, allowing easy front shifting and derailer trimmimg. #3 is with STI levers, up-shift and down-shift use the same motion, and I often shifted the wrong way. Bar-ends are different motions for different actions. I can pop off a rear shift very quickly, and my hands are almost always on the hoods or tops of the bars when riding. Those are my reasons, but then I know lots of folks that use STI and love them.