I personally use S2. I have Vixen and I have LSP. I think LSP can be a good piece of software, but has a long way to go. It always locks up on me and every time I try to convert a sequence, nothing ever happens. Vixen I personally find confusing. I know KC is working on a complete redesign, so maybe after that I will like it more.
S2 work great, has a lot of great features and I have never had a single problem with it. I am a beta tester for LOR and I get to see a lot of the features that are coming before the general release. What is coming, is awesome and will really set it above the rest of the software.
The major draw back of S2 for DIY'ers is the need for the iDMX. If you aren't using LOR equipment, the price of the iDMX will deter a lot of people...and rightfully so.
Greg