When I started in the auto repair field back in 81, I had the IR231. All around workhorse. oil it daily, and it lasted about 5 years of daily use in a professional setting. The IR231 was freshened up with a rebuild kit, and lasted another 5 years. Repeat process.
One thing I had on it was a bump cover. The 231 would be repeatedly dragged on the floor, fall off the lift, and just generally abused. The cover helped a great deal in keeping it alive.
I now have the IR 231, 2131, and a DeVilbiss. the IR's will probably last the rest of my life as I do not use them professionally any more. The devilbiss is a good tool, but no where near the power of the others.
It all depends on what you are going to do with them.
Also, it if is pnuematic you are going for, do not skimp on the airline filter and separator. Water and moisture will not prolong the life of any tool.
When building a diff on a D80 or 110, I will step up to the Snapon 3/4 drive for the carrier bearings, as it will make the job go faster.