here we go, you have probably just opened the can of worms which will get more responses than any other topic
the aim of all these products is to support your foot and spread the weight of your foot over a greater surface area than it currently is
the following is my opinion, there may well be others to follow
the superfeet product [which is the brand i use most, although 80% + of my business is custom] this product is designed to support the skeletal structure at the rearfoot, by stabilising the heel bone the footbed reduces any motion at this point, by doing this the arch supports itself, the priciple being simple, an arch is a self supporting structure, the shape in the product is there as a filler rather than a prop. the superfeet product often feels firmer under foot, this should not be seen as a bad thing, as too much cushioning is really bad as it can accelerate pronation
the conformable off the peg product works more on the passive support of the muscle system, for some people this works well for others it is like standing on a golf ball.
it all depends on your foot and what feels best, most stores should have demo footbeds of the OTC ranges they stock whcih they should be able to fit into your boot to let you try or at worst stand on the product out the packet and feel the differences.
let a good bootfitter look at your feet and make a recomendation, an OTC product is a good start, custom may be [but not always] better