The Tiffin is a gas motorhome (on the Ford chassis). 40k miles is not at all worrysome to me for the Ford drivetrain; the V10 engine should last, with reasonable care and maintenance, maybe 250k miles without needing major work, and the transmission is likewise generally reliable if given appropriate care. The house part of the RV is likely to wear out before the chassis. The same is true of the class C, for that matter.
As to which one you should get, assuming both are in good condition and free of leaks/water damage, I would suggest spending as much time as practical in them and working through the various daily activities you need to accomplish: go through the motions (at least mentally, if not in person) of cooking a meal, washing dishes, taking a shower, getting up in the middle of the night to pee, etc. You may find that one layout or the other is more suited to your uses. Also check how accessible things are with any slides slid in as for travel; sometimes it's mighty hard to get a drink from the fridge or use the bathroom with the slides in, and that can be an annoyance when traveling.
As far as driving goes, it's a bit different experience with a class A vs. a class C, but I don't think there's much intrinsically harder about one or the other. The class A is likely more maneuverable (or at least probably can turn more tightly), and you sit higher up which gives a somewhat broader view at times but can also amplify swaying and rolling sensations. The class C's cabover portion blocks vision upwards, which is nice if you're traveling into the sun but not so nice on a few other occasions. Both are wide and tall which takes a little time to get used to. On the highway, the difference in length is not really overly noticeable; it's mostly a concern when merging or passing or maneuvering in tight areas like parking lots or gas stations.
(I personally don't really see the appeal of an outdoor TV, or indeed a fancy TV/entertainment system in an RV in general. It seems kind of silly to me to travel to...well, most any destination...in order to watch television there.)