I use three programs in rotation; UF, Apophysis and KPT Fraxplorer. I used to use KPT Fraxflame but that was before I discovered Apophysis. I like being able to trade off programs, especially when I get into a rut. Lately I've been having programs making anything I like in UF, so it's nice to have something else to work with. Also, different programs give you different results and a different process. I find that UF is very complex and takes a lot of effort, whereas KPT Fraxplorer is more akin to doodling. Both are fun though.