We have a 2013 30.1 and love it. We've found the build quality and fit/finish to be fine. We've had a few nits here and there, but nothing major and certainly nothing that would dissuade me from the brand. (People complain about all brands and I try not to let perennial grumps influence my purchasing decisions.) The biggest problem we've had is that the Jensen TV failed, but frankly I was glad and replaced it with a Vizio. That was a couple hundred dollars. The ACE 30.1 layout is perfect (for us--YMMV), fuel economy is good (average 8.5 mpg, 7.7 pulling the toad), towing performance is acceptable, driveability is excellent, on-road comfort is excellent, etc. I note there have been some complaints about generator noise--we haven't noticed that problem. We are doing the usual number of modifications and customizations, mostly because we're incurable tinkerers, but you'll probably find your own list of little changes you'll make. You get the idea. All things considered, the Thor ACE is just fine for us.
One other point to consider--Thor customer/technical support is stellar. We've been RV'ing for over 30 years and had lots of contacts with manufacturer's reps, and Thor is by far the best. Thor even assigns you a "concierge" when you buy the unit who will check in a couple times during the first few months to make sure you're happy! I've called technical support a couple times (the most recent one just this week as I worked through the BCC recall), and I'm amazed at the courtesy and diligence I've seen. What a pleasure.
There do seem to be a fair number of complaints about build quality. As to such things, I'd be careful about such judgments. It's hard to get a valid evaluation of quality from reading online anecdotal reports, and it's definitely impossible from a personal inspection of a few units. If you haven't been following it, the worst nightmare I've read recently about shameful quality control and manufacturer indifference (even vindictiveness) pertained to a $400,000 Winnebago! (See
here.) FWIW, I'd think that the best way to address potential quality concerns is on the basis of a specific unit: do a thorough pre-delivery inspection, go over all of the major systems, insist on major items being right, and then keep a happy disposition and even temperament for the little nits as they crop up. Of course, that advice and a $1.50 will buy you a cup of coffee.
Having said that, I've heard very good things about the Jayco. And there a similar Forest River unit (called an "FR3," I think). We had a Forest River trailer and thought it was great unit. You probably can't go wrong with any of these units.
Feel free to PM me if you have any questions or if there's any other information I can provide. Good luck, and let us know what you decide.