Welcome to RR. There are really only 2 choices :GRE PRS600 and Uniden 996T or XT . RS is customer unfriendly, and very slow to incorporate firmware fixes and improvements. Uniden and GRE make radios for them, and the are both good about firmware updates, but RS delays firmware updates from both. GRE is the most aggressive and slightly better on customer relations. Also see: Digital Scanner Comparison Chart - The RadioReference Wiki
The basic considerations are as follows:
GRE is more sensitive(gets weaker signals), but that very feature makes them prone to overload if in the city or near any type of radio/TV/cell towers. Previously, GRE was better with digital, but I think that difference has been minimized with the latest firmware from Uniden...see how important firmware can be.
Uniden does not overload as much (hence is not as sensitive), and generally has more features, which you will probably appreciate once you are familiar. For example, they skip over encrypted communications, while GRE just hangs on them producing annoying noise. Also has GPS system control (limited value for a Base unit), and Fire Tone outs (limited value IMHO)
You really need software to program and better understand a digital radio. There is an excellent program for Unidens that is free: FreeScan. GRE typically costs $30-$40
You will find diehards in either camp, but I think they all generally agree on the points above, so you need to decide if you are far enough from the radio signals to justify a GRE.