We are on our second ACE and I have nothing but good things to say. We've had very little issues, it rides very nice for an entry level class A, no major failures, and Thor has been one of the best companies I have ever dealt with.
Frankly I scratch my head at a lot of the brand bashing that goes on around here. I think you usually hear bad things about Thor from folks who have never owned one. The full wall Schwintek slides were a black eye, but they aren't thor specific. Every brand that used them had issues.
As far as comparison, I can't say much about the FR3 as I've never owned one. I think at this price point you are likely splitting hairs on differences.