The PSR-500 and PRO-106 are the same scanner! There are two main differences, first is cosmetic - the button layout is different but all the same keys are there. Second is the firmware, Radio Shack gets a custom firmware for some reason. Nothing noticeable, they both operate exactly the same, but it does mean you can't use a GRE update on a PRO scanner you have to wait for Radio Shack to post the updates on their website.
I have a GRE (PSR-600) and both PRO-106 and PRO-197, like them all just fine. The reason I wound up with the PROs is they were a lot easier to get hold of (local store vs mail order) and I managed to pick them up during a sale that made them a lot cheaper than the GREs. Otherwise I'd probably have just ordered the GREs since then I'd be getting updates direct from the manufacturer, rather than waiting on RS. Last time I updated mine, RS posted the latest files quickly but that was some time ago so can't say how they're doing now.
Can't say anything about the Uniden, haven't used one.