I haven't used RISA Foundation, but I have used STAAD Foundation.
STAAD Foundation is basically a fancy GUI for the STAAD FEM engine. It's pretty clunky, the output isn't that great, the input is difficult (but a little easier than STAAD Pro). I haven't been too impresed.
If you have a chance to use something different, it's probably better not to go with STAAD at this point.