An Onan 5500 lP will be the most convenient option. Since your 5'er already has propane tanks there will be no need to: transport,handle, install or deal with gas cans of any sort.
LP gensets use more fuel than a gas unit, so if you plan on using your genset a lot you may prefer the efficiency of gas vs. the convenience of lp.
Lp genset are often more reliable than gas because they burn cleaner and do not have stale fuel and carb gumming issues.
On board is more expensive vs. portable however on board gensets are about convenience not savings.
No loading/unloading gensets. No security issues. No set up.
on Board gensets provide electric power at the push of a button. No cords,no keys,no need to go outside.
Just push the button and turn on the microwave and or A/C!