I've spent my share of time with both companies, tried to ride the middle ground and what not, but I'm not going to place nice to not hurt others feelings anymore:
Spyderco is better, hands down.
Much better company, first of all. Sal is just an awesome guy, constantly trying to improve his designs and materials and interacting with users, etc. Awesome warranty and customer service. Constant refinement. I could go on.
Now, the knives. They are just thought out for use better. They cut better, feel better in use, don't fiddle around with fancy liabilities like Benchmades do. You get more performance for your money form Spyderco, period.
Benchmades are flashy. They look nicer to a lot of people. That's really all they have going for them aside from Balis (butterfly knives). That is the only place BM gets the nod. Their balis are awesome.