It seems to me that it ought to be a combination. Take a salesperson who's great at opening up opportunities, but can't close them. Then consider an expert closer who can't ever open new opportunities. It takes a complete package (unless, of course, you're at an organization that has different positions for "openers" and "closers.").
In my opinion, the best way to evaluate salespeople is to come up with metrics that equate with your particular organization's needs and to then compare individual salespeople against those identifiable requirements. The more data you get and track, the better you will be at predicting the future (every salesperson/manager's dream). CRM can work wonders -- so long as it's tied to the way YOU do business.
"Selling is like shaving. If you don't do it everyday, you're a bum!"