454 engine vs. 460 engine
I would assume from your post that you are shopping used since the 454 is now known as the Vortec, even though it is the old 454, reworked and the Ford is not the V-10 which is actually a 10 cylinder 415 cid engine.
That said, you will probably find that both of those engines have an excellent track record and serve very well, although both are gas hogs. I would stay with one that is recent enough to have fuel injection as our first motorhome was just 1 year too old to have it and the mileage difference was about 15%. But either engine will last a very long time if it has been well maintained and both are very repairable. Generally, in those motorhomes, the GM chassis had a softer ride but poor handling while the Ford had a stiffer ride but much better handling. Both were good chassis but tended to be easily overloaded in the larger motorhomes. So watch the actual weight as compared to gross weight rating.