Mario,
Range is only dependent on a few things:
A). the output power of the source (the dispatcher's radio power per se). The more the better.
B). the antenna you're using (and how high you can get it- line of sight is ideal, the more obstructions, the worse reception).
Those 2 things being said, a scanner is only as good as it's antenna, and don't expect any range going into the purchase. Each individual users exoerience will vary based on what you like to listen to (weak, low power signals vs. hig power ones), you're location (urban, rural, b.f.e.) and habits (monitoring in a vehicle vs. a building).
Personally I like GRE products (though in all honesty, I've only owned one Radio Shack branded Uniden product). Their customer service is second to none. They're always releasing online product updates (the 8th firmware upgrade in 4 years. If you call customer service (I cracked my case and wanted to fix it myself, so I called to order the parts) and talked to a human. Their user interface is a very intuitive fit with me and many others. Again, you're going to get just as many users telling you to go to Uniden though. I know of more GRE users in the San Anto area than Uniden (myself included).
It'd be an interesting poll to see how many Texas users (we have quite a few die hard digital listeners here) use which scanners (GRE vs. Uniden). It'd also be interesting to see how this lined up to the different digital trunked systems.
