I have an '85 GMC that SMB retrofitted nearly 10 years ago with a 3-way Dometic fridge, and recently bought an '01 SMB with a 2-way Norcold. Here are my experiences with the two units:
1) Totally quiet operation, even in 12v. mode, which only drives a heating element, not a mechanical compressor.
2) Works great. Makes ice in 1/2 day. Cold even in Mojave Desert summer days.
3) I have never had a problem with excessive power use when in 12v. mode, but I always switch when I stop for more than a couple of hours.
4) Because it is propane, can run as long as the tank will allow. I have camped in Baja for over 2 weeks and never had a problem.
5) Because the fridge is propane, I have never needed solar panels.
6) I can bring unit down to temp using either 110v. or just light the pilot and let it run over night.
1) Requires that a vented hole be cut into the side of the van through with you light the pilot and turn the valve.
2) Of course (duh), you need to be plumbed for propane.
3) Requires switching from 12v. to gas when you stop and back to 12v. when you launch (takes about 10 seconds).
4) Van needs to be fairly level, but no more so that you would want for camping.
5) Sometimes the pilot is a bit cranky and hard to light if wet or dirty, or I'm trying to use a spark lighter. But so long as I keep the pilot tip clean and dry (if the road is real dusty, I just cover the little pilot box with a piece of aluminum foil); and use a long-snout, flame-type BBQ lighter, it lights immediately.
6) Some people don't like propane flame.
1) Doesn't need to be level to work.
2) Doesn't need opening vent panel in the side for lighting pilot.
1) Really loud compressor.
2) Power hog--mine craps the batteries in 3 days unless I run the engine, which seems stupid to do that just to run the fridge.
Considering all this, if there was a way to remove my old Dometic and install it into my new SMB, I would (I am going to sell my '85 and don't want to have a useless hole in the side of the van. I have been completely satisfied with the Dometic. It works perfectly, is quiet (important for me, especially when I am trying to sleep), and uses gas sparingly (like almost none at all). I don't have to mess with dead or dying batteries or buy a solar panel. Some people I have talked to find switching the unit from 12v. to propane annoying, but I never minded it. In fact, I sort of like the ritual when I get to camp.