Do you mean just for padding or for orthotic purposes (arch support, etc)? I use both, often together. For padding I like the cheap white foam ones from the drugstore. You have to replace them often but they are soft and don't make your feet sweaty. I find the gel ones hot and they are often oddly textured.
For orthotics I use either powerstep 3/4 or superfeet black 3/4 in most of my shoes. For sneakers and some roomy boots I use full length powersteps. These are all rigid and quite durable, I switch them between shoes and replace about once a year. Dr scholls type are useless, if you want real support you need rigid insoles. I buy them online but a good place to shop and try them is a running shop.
ETA: The powersteps are more supportive but bulkier. I use the superfeet in my slimmer shoes. I like the 3/4 length for both because they don't cramp the toes as much. I actually find they tend to make my shoes fit better because they take up some of the excess room in the instep! (Low volume feet here.) You might have to size up if you have higher volume feet and want to use orthotics.
I also put summersoles in some of my sandals. They are not padded but have a soft texture and cover up annoying stitching (I love born shoes but find their "signature" footbed stitching so irritating- literally, as it gives me blisters).
