All 3 are having problems with the SCR systems, they are simply problematic in general right now. Dodge only implemented the SCR system in 14, IIRC so you can still go fairly new and get one without, but they have problems with their DPF systems, which I feel is largely due to their heavy use of egr to avoid the scr setup. In any event all 3 have the system now, and all 3 are having their own share of problems.
GM has the worst placement of the tank, outboard of the frame right behind the right front tire. Dodge and Ford both put it up by the fuel tank, protected by a skid plate. The GM tank is the lowest point of the vehicle.
If it were me I would look at the used market (Ford 6.4, or "bulletproofed" 6.0 (there are delete kits that keep the "cooler" in place, but block it off on either end and just allow coolant go through if you have visual inspections) or Dodge 4th Gen, either motor), and if I were adamant about buying new, Ford has EGR cooler problems and they seem to have sorted out the other issues (the earlier ones had some head issues) and the Dodge 6.7 has head and EGR issues. Also DPF issues galore. Ford will keep a front end in it a lot longer. But I'd pick between those two for sure. GM is great for staying on pavement and towing a retiree RV or something. They're solid pavement Queens and they haven't really messed with the 6.6 duramax for a reason. Typical GM evolution vs redesign.
Sent from my SM-G870W using Tapatalk and edited for clarity on my PC.