For tools such as angle grinders that get used sometimes for an hour or more non-stop, it is best to buy quality tools, not big box store stuff. Unfortunately, it's not so easy. You have to buy them used. Strange to say, one of the best lines of tools I have found were the Black and Decker Professional line. (I guess B & D got such a bad reputation with their home handyman junk that they could no longer sell their good tools.) The best tool brand ever, bar none, was Sioux. They quit making electrical tools when the Japanese took over the market. Milwaukee was a great tool too, but now that AMC owns them I suspect they have done the same to Milwaukee as they did to Harley Davidson during the years they owned them.
I look for Sioux tools, old pre-AMC Milwaukee tools, and B & D Professional tools used. I buy them when I find them. They never wear out so i give them to my friends.