IMHO, the answer is not something that can be limited to one tool only. I have a 1" belt sander/grinder, large slow wet wheel, regular grinder with two wheels and a slow grinder with an 80 grit for sharpening. I'll go to the one that suits the job at hand the best. Used or inexpensive grinders can be bought without breaking the family budget. The 1" belt sander, with a disk is inexpensive. Mine is sold under a variety of brand labels. I have (surprise ) a Grizzly. If you're limited to one only. Go to a flea market and buy a used grinder.
"Folks is funny critters."
Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire