Ford or Chevy.. That is kind of like asking which church you like best (I am Catholic by the way, but let's not discuss that, You are, of course ___(Insert your choice here)____.)
There was a period where Ford had a problem with the V-10 popping spark plugs out.. And some body builders so box in the 8.1L Chevy Vortec that the plug wires overheat.. (others do not)
By now the plug problem, if the RV you buy had it, should have been fixed, (Fix is fairly easy from a technical standpoint and) and the cooling kit added to the Chevy engine if it needs it. So either would be good.
Personally.. I'm also a Chevy fan, or to be more precise NOT a Ford fan.
Oh, when it comes to transmissions.. If you ask who makes the best tranny.. The shouts of ALLISON will drown out all others... On that I"m sure. .Even Ford admits the Allison is best and that's one I can not argue with, since they do not make it (They make "Our answer to the Allison" though, but of course.. It is not as good).
I know an engineer who was involved with the Allison design