Most of my locations are on the systems baked into the SDS. I do have a few DMR systems, so I bought that key as soon as my unit arrived.
There are also a few NXDN. Not many, but a few.
So not rushing into things, I waited until I had another $50 burning a hole in the wallet. I bought NXDN a few weeks later.
I have not loaded NXDN yet.
I did find some of my PDs have DMR and in Western MA, there are a handful of DPWs, and other institutions that are DMR. Supposedly, DMR will expand in time as more non-public safety municipal communications go to DMR.
So I would say at this point, DMR would be one to look at. Check RR listings for your area.
I let you know if anything good is found in my area on NXDN. Then, I'll be able to tell you if it was worth it for me. (Again, depends on what is in your listening area...)