I'd say they're comparably good, and I'd point to:
http://www.82games.com/0809/CSORT11.HTM
Both have their moments.
Rip can play both wing positions in a pinch and can defend at SG. Gordon is a volume 3P shooter who can't defend at either guard position. It's funny how Rip put up his career averages without an All-Star PG. Rip can actually get open. You can't just put a bigger man on him and turn him into streaky jumpshooter boy (though in Boston's case, their bigger guards kept on fouling him from beyond the 3P line). They're both somewhat turnover prone.
We better get someone good and big for Rip, or else we have another broken situation. I'm not opposed to getting rid of Rip, but Ben Gordon will be a step down come playoff time.