I am currently working on a custom toy and a miniature Dwarf King and I am using a new cheaper brand of putty that worked really well.
I'ved used a lot of different brands of industrial grade putty for my hobby needs, although I still use hobby grade putty for more refined projects. In my humble opinion, Tamiya putty, Green Stuff and other hobby grade putty are best as they are smoother when cured and are all very manageable.
However for bigger projects like the BUTT of my custom The O, using hobby grade putty will cost you a bomb! I suggest you use industrial grade putty to get the general shape and cover it with hobby grade putty for a better finish and for better handling and sculpting.
I highly recommend the Selley's Aqua type putty as it is so far the smoothest industrial grade putty after curing. However Selley's is twice the price of other Aqua type putty brands.
Just got my hand on this new V-TECH AQUAFIX All Purpose Putty that looks so much like Selley's, handles like it and cures almost as smooth as Selley's for HALF the price! Needless to say, Selley's and this new V-Tech Aquafix is way better than the more popular Pioneer stuffs.