I shoot more soft plastic than I do any other firmness but then I specialize in the smaller baits. I think for the sake of toughness, I'd suggest the medium in a worm. You'll hang onto great action yet the bait will tolerate a little more of a beating that a bass can hand out.
I do shoot some larger stuff for walleyes, mainly the Ring-It 4" and the Thump Grub. I use the soft plastic in both of these because they see much colder water and the soft formula plastic keeps things real active without a ton of angler induced activity. Both baits done in soft have enough action without much help from me. I do give up some durability with the soft though.
I really recommend people getting a qurt of the soft and a quart of the medium if they are starting out and use both to see how things come together. Still, if only one firmness is preferred, get the medium and a small bottle of softener to use where a softer plastic might be needed.