People often recommend using super sculpey firm, however, the consistency of both products is often skewed. I bought used Super Sculpey more than Firm because it was much more hard, didn't act like gum when you had been working with it for too long. Firm would act the opposite, so I stayed away from it. I sometimes mix the two because they compliment each other well (both color finish wise, and sculpting wise), but I later found out that Firm is usually the tougher product. I got a bad batch of both of them, it turned out.
So, I'd suggest you get both, just to be on the safe side. Super Sculpey Firm is used more often by professional sculptors. Make sure you have the proper tools (I have hundreds), and make sure you feel comfortable working with a specific product. I didn't switch to Super Sculpey until trying out several others.
For touching up areas and what not, a lot of people (including myself) use Fixit/Apoxie sculpt. Sculpting into it is a pain, however some people have adapted themselves to how it works, due to the product being incredibly durable once cure. I only use it on areas which need to be filled/flat surfaced objects which I can sand into. Working into it once it's cure is a dream, it sands very well and can be cut very nicely.
