My usage is mostly auto repair with some wood thrown in. I'm not a pro-level user by any means, so YMMV.
My most used are the 3" straight and angle die grinders, followed by the air chuck and blow gun. Further down the list are the brad nailer, 6" random orbit sander, and an air chisel. Have an air ratchet, but think I've used it twice in 20+ years, occasionally use a 1/2" impact for tire work.
My die grinders are Harbor Freight units and have been used, abused, and have held up way better than I expected. As others have said, they are so cheap just buy several units and keep different bits/arbors in them you can grab as needed. I find I use an angle head grinder 90% of the time.
Air chisel, my cheap one (Campbell Hausfield?) works pretty well for busting up bathroom tile, but ***** for knocking out rusty suspension parts. Wish I got a better one, but don't use it often.
Impact, again mine's cheap (think it came in a starter kit with the chisel). Gently taps on bolts instead of actually hitting them. Don't use it very often (hardly ever), but plan on spending more on a better air or cordless unit.
Brad nailer - got the el-cheapo HF one for ~$20 to put down some baseboard trim. Don't know why I didn't get one years ago. Awesome for tacking up cabinets before running in screws, knocking together some wood fixtures/jigs. I'm sure there are better units, but have been very pleased with this one.
The sander is used on refinishing furniture with finer grit paper. Think it was a house brand I picked up through work. Not as comfortable as a palm sander, but also ~1/3rd the cost.
Didn't care for the air chisel - found it was too much hassle to get it where I needed it, was too noisy, and too bulky overall. Seemed like the hose was always in the way. I much prefer the tactile feel of a good hand ratchet.