From personal experience I would choose the Rival only because I find it more comfortable. None of the Logitech mice are comfy if u ask me, but that is just personal preference. Even if Rival 100 has a budget sensor and lacks the 400 dpi step I played better with it. For me the shape is the most important!
I have tried around 40 mice (mostly for fun) and I can tell you that it is really hard to say exactly what fits you. The easiest way is to try them out for yourself.