Sorry is the PSR 500 you mentioned the same as the 500 I posted about? Also I should ahve mentioned I want it handheld?
Can I ask you, why those choices. Dont' know much about them, trying to educate myslef as we speak.
Although I don't think the City of Miami PD is P25(Need to look in the DB), several systems around your area are P25 Digital and the 500 and 800 seem to handle P25 Systems better. (Just my Opinion) I host 6 feeds, all with GRE's except one feed. I had nothing but a positive experience with both those scanners.
The GRE 800 handles X2 TDMA Systems which no other scanner does at this time. I don't think you have any X2 systems in South Florida, but it's good to have it in case you travel to a region that has it or will have it in the future.
Both are Handhelds. One more thing, if you are new to scanning, I think the GRE 800 is the easiest to program if you are not familiar with programming radios. The 800 is a little more, but worth the extra I think.
With any scanner, GRE or Uniden, I recommend you buy the radio shack 800 mhz Antenna(If you monitor primarily 800mhz systems). The antennas that come with the radio's are crap.
Some Prices I have found below:
GRE PSR 800: h ttp://www.ebay.com/itm/GRECOM-GRE-PSR800-Digital-Triple-Trunking-HANDHELD-POLICE-SCANNER-PSR-800-NEW-/260939820781?pt=LH_DefaultDomain_0&hash=item3cc139aeed#ht_2840wt_1270
GRE PSR 500: h ttp://www.ebay.com/itm/GRE-PSR-500-HandHeld-Digital-Police-Scanner-APCO-25-BRAND-NEW-/270934478666?pt=LH_DefaultDomain_0&hash=item3f14f40f4a#ht_2037wt_1270
Here is the antenna :