I have both the Pro-106 (same as PSR-500) and the GRE PSR-800. Love them both for digital, so it depends on your hobby preferences (although I find the 800 more sensitive). If you like more traditional scanners with the ability to program on the fly, have full control either via keyboard or software, then the Pro-106/PSR-500 would probably be a better choice. If you want a less complicated (and less hands on) experience with the entire US database on your radio with the ability to set up playlists and select them, but no direct entry capabilities (without a PC), then the PSR-800 (or Pro-18) is a better choice.
Both have their pluses and minuses, but I don't think you can go wrong with either choice. As I get older, my preference is quicker and easier, so I lean towards the 800.
Good luck with your choice!
Bob