It depends on which kit you use to do the conversion. Some are propane only, some dual, and some are tri-fuel (gas, propane, natural gas). I think it kind of depends on how you use your genset as to if it's worth it or not. Initially, it's a pretty spendy conversion.
If you only use your genset for rare emergencies, then propane might be a better option. Mainly because propane doesn't go bad on you like stored gas can. It burns cleaner, extended running is easier with a 20# propane tank, and you'll spend less on maintenance.
On the flip side, gas is more efficient. You'll get the maximum rated wattage out of your genset. Gas is more readily available, and while you'll spend a bit more on maintenance, you also save by not paying out for the initial conversion. That's a lot of oil and filters.
I have 2 Yamaha 2000is's which I run on gas, but I also built my own 6gal dual extended run tank, so that's always an option if runtime is a concern. Mine aren't sitting in the garage for months on end though so for me the conversion isn't worth it.
If you are a prepper though, I would definitely go propane.
Hopefully that wasn't too convoluted.