It all depends what you like but my experience going inside both was the quality on the Winnebago was way better but Thor seemed very nice for the money.
As an ACE owner I will attempt to shed light where I can. First are you comparing the MSRp's? Thor and their dealers heavily discount ACE's. You can buy a 29.1 in the 60k's and a 29.2 or 30.1 in the 70k's loaded (paint/jacks). From what I have seen, there are no such deep discounts to appeal to the entry level market on the Vista. From a MH perspective you are really comparing apples to oranges. The ACE has an electric bunk and can sleep 8. Looks like the 26p might sleep 4. The Winnie is smaller but 2 slides. The floorplans are very different. The ACE is a sort of niche market. It is arguably the lowest priced Class A. However it's based on a Class C concept and has a bit of that hybrid Class A with a bit of Class C feel, fit and finish. Owning an ACE I must admit that the fit and finish of the Vista is better than the ACE. (just walked through a vista last week)Each is built that way to find their own market. I also wanted a coach that could handle more abuse. Less carpet, almost all the floors are solid surface etc. I also bought the ACE because I wanted an A but a Class C price tag. The Vista Market demographic has accepted the price of an A but want better fit and finish than most starter, entry level coaches. Bottom line, the Vista is a better quality coach, at least in how it's assmebled and products used(same chassis) But you won't find a better value than the ACE for a 30' Class A. You want a shorter coach with 2 slides and better fit and finish, get the Winnie. You want lower price in a bigger coach that sleeps more, get the ACE. And don't get me wrong, there is plenty to love about the ACE. It drives fantastic, there is less carpet to get ruined, Thor is awesome, the electric bunk is a huge hit with kids, TONS of storage, I mean TONS, and it's cheap. That said it does hold it's value remarkably well. I could sell my ACE after a year for just about what I paid for it. Try that with any other 1 yr old coach. Winnebago makes a nice coach, but frankly I think they are overpriced despite the better finish. That bigger price tag also equates to more depreciation.
Excellent analysis of the two. I agree from looking at them. The Thor provides a lot of value and gives you the A feeling with a bit of C. For people with kids, especially younger, that bunk is a wonderful. Several others have included the same concept. I am pleased to hear it rides good as I have not driven one. As in most of these it depends on your needs and how to maximize them at a good price. I like the exterior look of the Thor.
I own a 29.2 ACE and have it stored right beside a Vista. To me, the looks of the ace blow away the vista. I've never been inside the winny, but I would hate to pay more for it than my ace. The ace drives fantastic. The electric bunk is nice even if you don't have kids - we put ours down when we camp and put all our junk up there to get it off the floor, etc.