I went through this a few months back. I spent a lot of time going over specs of different radios ( brands), etc, looking for the right combination of features ( for me). I wanted Bluetooth ( preferably dual, so 2 phones could be connected), knob for volume, navigation with Turn by Turn voice and Lane Identification for turns, Sirius capability, Bose compatibility, Back up camera ( dual camera a +), HD radio as an option.
Many offer navigation, but only a few offer Garmin navigation. I have used Garmin in the past, and was comfortable with their features, so thought that was best. Many of the Nav's offered do not have turn by turn. Some offer it on one model, but not on other's ( Jensen 7022 vs 7021). All required an ability to download upgrades via Windows ( I don't have a windows computer- chromebook all the way). I finally decided to try using my phone for navigation, as many of those programs can be mirrored on the radio as well. I thought this might be prudent, as there are so many available now ( Google, Waze, Navmii, and a bunch of others, most of them FREE). There are new offerings almost monthly. One feature I like on some of them is you can download the maps to your phone on WiFi, and the use of data when you are driving is minimal. You also get up-to-date maps this way, vs having to pay each year for an update ( that is already a yr obsolete when you get it). I like Google Maps, but they do not currently mirror on the radio. I tried a couple of others, and settled on WAZE. Very similar to Google Maps, and once connected, everything can be done from the screen of the radio.
Once I had decided the above, and decided that HD radio would be a nice feature ( should I not want to continue with XM), I leaned toward the Pioneer model AVH-X3800BHS (AVH-X391BHS). If you are going to stick to XM radio, then the AVH-X390BS would be the same model less HD. One reason I selected this is that Pioneer offers an add on module for navigation, should I determine later on that I did not like dealing with the phone for NAV. Only negative for me is that the radio does not have a knob for volume ( buttons instead), but I find that I use the steering wheel controls most of the time anyway.
I installed using an RP4-GM11 adapter. It is essentially the same as the RP5, but uses RCA plugs to connect to the radio for the speakers ( Vs soldering a bunch of wires). The other difference is that the RP5 also integrates On-Star, which I don't have ( and I don't think the SSR came with). You'll Need a GM antenna adapter, and a mounting kit.
If you have questions about other models, I may be able to give some input ( I can look back through my notes)...
HTH
