Really and truly depends on how you camp, though I would go with the external gensets.
For me and pardette (wife) we do a lot of dry camping. Down here we get plenty of hot nights most of the year. No power, no AC. When we dry camp, having the gensets is great. Biggest problem is that ethanol fuel derates the gensets. You might have to run gensets out of eco mode because they cannot ramp up load fast enough when the compressor kicks in.
Onboard gensets are nice for a variety of reasons. One of the best is remote start. You can leave the AC on in the RV with the genset off. When you get close to a rest stop for lunch, hit the remote start power comes on and so does the AC. You have a cool trailer for lunch.
Onboards are also nice since little setup is required. That is nice when camping at Camp Wally World. On our last trip (2.5 weeks) we spent 6 days in truck stops, rest stops, and Wally Worlds. While I don't have an onboard it takes me about 20 minutes to lineup gensets, tanks, cables. I can do it in as little as 10 minutes.
The advantage of externals is that they can be used elsewhere. It is nice to have generators when we work the range and I can drag around one of the 2000s to run the pole saw.
Generators also give you lifeboat mode at home. During one of the last hurricanes we were without power for a couple of days. I stayed in the TH with AC, satellite, and complete comfort. The mother-in-law who lived with us, God rest her soul (great lady), I could not convince to come out to RV! She said, "You aren't moving me out to that trailer. I said I would never live in one those and my daughter will stay with me!"
So my wife stayed in the house, sweltering, while I and dogs (no fools they) stayed in AC comfort.
So a generator will give you options you do not have, but if you really aren't going to boondock I would not get one.