My opinion:
Super Sculpey is great for beginners. It may be a bit soft for those who have firm hands in which then I recommend Super Sculpey Firm. I use both. Sometimes mix and match. You endless things with these including baking a whole piece or baking in layers or baking the body and adding super sculpey with a dab of vaseline(this does wonders to stick the sculpey onto anything baked) and proceed with a heat gun. More experience and time recommended for that process.
Apoxie Sculpt is really nice. I use to use this as well. It is good for the armature and for detail work to put on top or to do a quick sculpt or a sculpt that you want to let cure and sand and add more and repeat.
Magic Sculpt I currently use in conjunction with the sculpey products or by itself is awesome. I personally find it a bit smoother and a little less grainy then Apoxie Sculpt.
Now keep in mind that if you use Apoxie/Magic Sculpt for amature that it will make your sculpt much stronger but it comes with the price of weight. If you have a sculpture that is very dynamic and not balanced you will need more weight on the bottom. But as you gain experience you will learn to balance the sculpture so no matter the weight and material you can find a way for it to hold its own. The armature is just as improtant as the detail process because it can determine how much time you will spend on your sculpture and sometimes the amount of material needed for the project.
I hope that helps.
-Jon