I've been using RASP's, BLIPMaps and XCSkies for a number of years.
As our RASP coverage in Central California has improved, my faith in
XCSkies has waned. In our area we have a marine airmass and an inland
airmass with somewhat complex topography and I don't think XCSkies has
the resolution in its underlying models to deal with those
differences.

For us, the RASP's are generally the best, though the full BLIPMaps
NAM often are better predictors of max heights or clouds.

I do subscribe to XCSkies though, it's worth supporting anyone trying
to build these tools since it is the only way to expect them to have
the resources to improve. The interface is great, even if the output
isn't terribly reliable for us. I do find that it is very optimistic,
so if you're looking for motivation to get excited about the weekend
it can be a great tool.