I own a disc brake road bike. It's my primary commuter and I have nearly 9,000 happy miles on it so far.

Yet, I agree with the other posters here. If you don't *routinely* ride in the rain and snow, disc brakes add only unnecessary weight, expense, and maintenance.

If you do routinely ride in rain and snow, disc brakes are *very* nice to have, but I'd avoid the low-end brakes on the models shown.

The heavier hubs and rotors on disc brake bikes add weight at exactly the place you don't want it--rotating mass. They add expense, which at the budget end of the product lines, means savings have to come from someplace else--usually in the form of cheaper (read: cheesier) wheels and drivetrain components. And they add maintenance--I'm forever truing my rotors so they don't rub.

In that $500-$700 range, you'll get a much better bike if you can drop the disc brake requirement. If you must have disc brakes, wait while you save enough to afford one with Avid BB7 brakes.