For field use, where I'm not really interested in any cushioning effect, my choice is the Pachmayr Old English. It has a nice simulated leather texture and comes in a variety of sizes, thicknesses, and I think black and brown colors. It looks good and protects the buttstock.
Except for clay target work, I avoid the soft, sticky, clothes-grabbing Decelerator and Kick-Eez type pads. They can be tricky to grind if you haven't done it before.
Someone above said the Silvers type pads are just a big chunk of heavy, hard orange rubber. It's hard to argue with that, but they can look very good.
If one needs recoil reduction, the Hawkins-type reproductions as noted above are a nice choice. Though made of a firmer, non-tacky rubber, they nonetheless have a bit of flex and can add a nice touch to that old Smith or Fox.