Hi Hemi -
I've had both the Ford and the WH engines.
The Ford was on a 2000 32' Rexhall chassis, and ran like a dream. Very smooth and plenty of power to pull a Wrangler, and (if I remember right) it got about 7.5-8 mpg at 60-63mph. Finally sold it because it cracked a head at 37K+ miles - no advance notice and i couldn't find any other similar failures even after an extensive web-search (maybe it was my Saturday-nite drag-racing that did it
). Ford picked up most of the tab so I was happy with the outcome, but i was ready to go to a bigger rv anyways. I loved the sound of that V-10. Neighbor has the V-8 version in her Expedition, and still I smile every time she fires it up (at the engine, NOT at her!).
The WH was on a 2004 38' GulfStream chassis. Only had it about 6-8 months and 4k miles, so I can't say much about it. It had a bit more pulling-power but fuel-economy was worse, if anything. Felt and sounded like a V-8, and a bit more vibration.
All and all, probably a toss-up to me on engines. Some folks are having issues with rainwater-ingestion on the V-10's, something to do with the way the snorkel is designed. I never noticed it on mine, tho. Both Ford and WH customer-service get a thumbs-up from me.
Not sure what years you're looking, but the transmission might be something to look at too. The Ford had the Ford-tranny (well, duh!) that's been around for years, while the WH had the Allison. I liked the Allison very much, it simply acted like it was more heavy-duty.
And, since you seem to be looking for something that's been 'previously-loved', I'd say the care that went into EITHER one would be a major concern.
HTH,
Ron