Also know that Vixen is due for a major upgrade this year (version 3.0) that is going to change quite a bit (gone are plug-ins, in comes modules, for example). I know that Vixen is trying to be more RGB friendly and moving towards what the trends are in animated lighting (aka smart strings and coros, etc.)
The two mentioned software packages (LSP and S3) are probably the most mature and stable for RGB/smart string support (IMAO) at the moment. Realize that S3 and LSP are not free.
The advantage that Vixen has is large support base (however, LSP and S3 has just as large of a support base, IMO) and that it is free. It just lacks some of the cooler new tools to support RGB and smart strings at the moment. Also it's scheduler is still not quite where it needs to be (IMO) at the moment.
Hope this helps some.
Kurt