OS X Snow Leopard – if you’ve got an Intel based Mac, get Snow Leopard.
I installed it Friday. Install time was about an hour and 15 minutes. In my case, at least, no glitch so far. It freed up about 7 GB of disk space, and everything runs noticeably faster. Many things open up much faster.
For an upgrade cost of $29, it’s a great value. So far, I like it!