I thought
www.dynabrade.com made about the best die grinders and sanders. Have some at work and they are nice.
I've also used industrial quality
Ingersoll Rand grinders and they are great quality too, and like Dynabrade quite expensive. the long reach 90* with about a 3" cutoff wheel (or grinding wheel) and guard is really handy, not sure the model but that's what I used most, I'd like to find a used (cheaper) one now...
Day after day at another job I used a
Cornwell angled die grinder/sander and a different one for a cut off wheel. I don't see the angled one that I like on their website, but aluminum housing with the blue grip on it and gearless, less than 90* angle. No problems and we had 4 or 5 of them in the shop, used them all everyday for sheet metal/rust repair and replacement work.
The better quality Cornwell grinders are a great valve, I'd buy more of them.
I'd stay away from the cheap geared angle ones that you're likely to see a lot of in your searches, the gears don't seem to hold up so well. Have not had or heard of any problems with the really good industrial quality versions, other than the significantly higher price.
Grigg