I'm not an expert sculptor, but I sculpt figures for my own gaming and amusement. Here are my thoughts:
Green stuff is, in my opinion, the easiest to work with overall. I primarily use this for sculpting objects on bases, adding items to figures like bags, hoods, and clothing, and I do most of my initial figure build up with green stuff. Is it as hard as brown stuff? No, but it cures hard enough with a little flex after it cures. I'd think that you would never have to worry about something snapping off if you dropped a figure made of green stuff.
Brown stuff isn't bad, but after using both I ultimately gave up on brown stuff. That is mostly because I felt I could see my work better in green stuff. The details popped out better for me.
Apoxie sculpt. This is, by far, my favorite. It cures rock hard (I would worry about shattering if dropping larger objects), it is much cheaper than green/brown stuff, and I can buy it in sufficient quantities to allow for doing things like push mold cars. It also sands well. In its workable state it behaves more like clay, which is also nice for doing detail work. It has a longer workable time than green stuff, which is also nice if I want to mix one batch and then work on several things over the course of 1-2 hours. It will start to get tougher as time goes on, but I've found it workable almost out to three hours.
Pro Create. I bought a bit on a whim, and it has been ok. I'd say it cures up faster than anything else I have worked with, so I could feasibly do 2-3 additions in an afternoon with adequate curing of base layers while working on top. What I don't like about it is that it is also the least likely to adhere to base layers.
Green/brown stuff have a tackiness to them that I like. Apoxie is even stickier at first, but then loses that quality as it cures.
I'm sure others will have a more educated review for you, but I would say that it might be worth trying out Apoxie Sculpt. It hardly matters what a pro can do with a product if you (and/or I) can't get the same result. In the end it has been useful, to me, to just try a whole bunch of products and figure out what works best for me.