There's a lot of comparative info on pads and resos, and other stuff, at www.musicmedic.com.
Griff, I tend to agree that the resonator material isn't that important. I usually go with the brown plastic ones, as large as will fit the pad. That way there's nothing to corrode or rattle or any additional weight.
Some of those waffley looking gold-plated resos would be pretty cool looking for a younger guy, or maybe somebody who likes to show up in gold lame' suits and sequins and stuff. Personally I like to keep it kind of discreet - in accordance with my talent, i guess.