Both companies make excellent products. You'd be way better off decided which particular Spyderco and Benchmade knives you're interested in, and then telling us what you'll use them for, and then asking about those two knives specifically. There are any number of knives I'd give Spyderco the edge on, and any number of knives I'd give Benchmade the edge on.
Most of my carry knives these days are Spydercos (spydercard, endura, calypso jr.), but my favorite 4"-bladed folder ever is a Benchmade (710).
Joe