From my experience, ProCreate is about the same price than greenstuff, actually slightly cheaper. Note that ProCreate is sold under different labels (e.g. Gale Force 9 grey stuff is procreate).
The two are not so dissimilar. ProCreate has a bit less memory and feels a bit stiffer but the difference is really subtle. If I have to sculpt anything vaguely detailed, I include some Fimo in the mix. It changes the consistency of the putty quite a bit and it took me a while to get used to it. It also increases curing time, which is something you might not like. Though, if you're in a hurry you can always accelerate the curing by putting the sculpt in the oven at 50°C, putting it under hot water or using a lamp.
Below, some other tips that allowed me to improve on my sculpting.
I use vaseline to get smooth surfaces (just a very tiny bit), it works far better than water (or saliva). I also wash the sculpt regularly with warm water or soap between steps. If you use silicon shapers, there's no need for any lubricant.
Don't compromise on the armature. I build my own by soldering fine wires (between 0.5 -1.00mm and 0.2mm for hands). It is time consuming and a bit tedious but a good armature really helps improving the final result.
Finally, probably the most critical factor for me is a good source of light and a magnifying visor, as I otherwise just can't properly see what I'm doing.