Note: There are are belted and non belted pads. Stuck on pads are usually only found on really cheap trampolines. A good belted pad should cover all the springs but have the old way they are connected. Most pads are about 15 inches wide with some that are up to 20 inches wide.
Some pads are made with closed cell foam and others are open cell. Beware of really thick looking pads that are not dense enough to absorb the ballistic impact when theres a fall. The whole reason for pads in the first place is to absorb ballistic shock. Some pads lose their resiliance and absorb less and less ballistic impact as the pad ages. Closed cell types don't flatten out as much as open cell types.
Foamed pads can either be coated with vinyl or naugahyde. If using vinyl, I try to stay away from anything less than 18 ounces and must be UV coated. Some cheaper vinyls can crack in freezing weather and tear. I've seen trampolines with duck tape all over it, usually the ones with lighter duty vinyl.
If there is a tear in it and water gets in, it can rot and mildew, that is why I like the 18 ounce and over covers as they are less likely to rip, especially when my 260 lb neighbor comes over.
If getting naugahyde, then it really doesn't matter. Its so strong. This is what the most expensive boxing gloves are made out of. On cheap pads, over time you can feel the springs by stepping on the pad. I do not like models where I can feel a spring with my bare feet when standing on a pad.
I try to avoid thick soft type open foam pads. When someone calls and just wants a thick pad, they usually haven't done their research. Stop trying to cut costs and make a closed foam pad when you know parents would prefer that for their kids if they only knew what to look for.
Note: make sure that the pads are wind resistant. You can have the best pads but if the wind blows the off, then its not good. Also know the foam density ratio to thickness of the foam.
If you are concerned about padding, let me know on my quiz. The heavier the people bouncing are, the thicker the closed foam is preferred. If for light weight kids, then, depending on how wild they are on the trampoline, open foam can be ok. Take my quiz below and I will help you pick out the right models based on your answers.