It's a shame most of the secret characters get really overshadowed by mandatory ones like peter and slade. Well, slade is kinda garbage for a while but becomes a glass cannon pretty quick and always has good movement so tends to get a lot of kills. I always wanted to use the cool characters like the wolfman and the robot and rare promotions but they're all mostly kinda crap.
If i remember right - Slade and Peter are obvious powerhouses, but other four "unique characters" certainly have a place in the party - Geralt, Zync, Klaud and Kiwi. Kiwi being the biggest stretch.
I mean, the game isnt hard really, and you have like 12 spots.
1 for the protag (Bowie), six for uniques - Slade, Peter, Geralt, Zync, Klaud and Kiwi. And you have five spots left.
I usually take the starter team (Sarah, Chester, Jaha, Kazin) for nostalgia reasons, slap them alternate promotions, and still have a spot left. The 12th usually goes to the semi-unique centaur, May, but i occasionally swap her for the scary elven wizard. Luka if you really need another flyer, but you already have 3, so eh.
But yeah, the game isnt that hard, you can pretty much take characters by using rule of cool, and still breeze through the game.
Now, couple years ago i beat the full SFIII, and I was under impression that it was excellent. Need to give it another chance obv, but I'd say its certainly worth a shot.