I posted my own observations of the ACE vs. FR3 on a post over on irv2:
http://www.irv2.com/forums/f254/fr3-149400-2.html#post1559104
partially copied below as well.
Regarding MikeBreeze's comments about the ACE having a king bed - one of the ACE models has a king, the others do not. The ACE 30.1 model most closely mirrors the FR3 30DS, with a split bath floor plan.
The ACE has 1" sidewalls compared to 1.5 on the FR# (stronger, more insulation, etc); The FR3 is made w/ heavier gauge aluminum; In the FR3 they run the "Plank wood style flooring" over the entire subfloor - even where there is carpet - which creates an added moisture barrier should there ever be a spill or leak from above; Also, I noticed more care given to securing wiring and water lines, attention to detail on trim parts and that sort of thing.
On the design front - the FR3 has a radius roof (more room in the front drop-down bunk), flush floor construction (no step up into cockpit), a double sink instead of smaller round sink in ACE, Flexsteel furniture - far superior to the furniture in the ACE; full queen (60x80) instead of small queen in ACE (60x75); the front cap in FR3 has smaller pillars compared to the larger pillars in the ACE which create more of a blind spot.
The product manager at FR was quick to give credit to Thor for the initial design of the ACE - after all, they got this type of hybrid product to the market first. But then FR built their own version very similar to the ACE, then tore it apart and rebuilt it to improve upon it, and yet again, until they were satisfied they had a superior unit, and I believe it is.
