I use Aircat 1150 and am well satisfied with it, I had the IR 2135 TI max and wasn't happy with that gun at all, it started out well enough but soon became gutless and rattled apart. The old IR231 was a great gun but its not sold anymore just a Chinese copy of the original.
There are other guns that I would say are better than either just from using them but they are difficult to obtain in the US so its sort of pointless mentioning them. If you want to import them, the Hazet 9012EL-SPC and Atlas Copco W2815 pro are better built are as strong if not stronger.
For the $$ the Aircat 1150 gets my vote, do not buy the 1200 with pin clutch mechanism, they are not well suited for automotive work, twin hammer only.