I'm a fan of the thick foam RedOctane dance pads. I've used the cheaper, thin ones from the store and found that they slip all over the place and are harder on the feet. The metal ones caused me to get sloppy, because my feet tend to roll outward a bit and I couldn't "feel" where the buttons were through my shoes. The foam ones could be used in your socks, and were squishy enough so my feet didn't hurt after jammin' along for awhile.
<---those are the kinds of dance pad I'm talking about. I doubt you can but it anywhere but online--I know you could probably find a version cheaper on E-Bay, but at least buying it through the maker, you know that you're getting what you pay for!
I started out with just a PS1, so I started with the Konamix version of DDR. I've also used DDR Max and DDR Max II before, and I like them all--though Konamix has a special place in my heart
is a deal they have running for 2 foam dance pads + DDR SuperNova for $200 (where a single pad is like $80...so if you're buying more than one, I'd look into it!)