They all seem to do about equal in performance if you're just looking for speed and distance. Your biggest decisions will be if you want more info such as max speed, average speed, cadence, and the list goes on... Plus the corded/cordless decision. I preffer the cordless(especially on suspension bikes). The issue there is that flashing lights, such as the led tail-light i have, will cause your speedometer to go nuts.
If you are new start with a Cateye or any other bike shop unit. About $25-$30. It will not be wireless or have cadence. On a suspension fork, run the wire down the brake cable. It will do everything else. Speed, max speed, 2 trip odo., total odo., average and timer/clock. Do not buy whatever Walmart or any other dept. store has.
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