You can't compare 6" grinders with 10" and 12" grinders. They're intended for different purposes. A 6" grinder is excellent for sharpening small tooling--lathe tool bits, drill bits, chisels, etc. 10" and 12" grinders are for removing large quantities of materials from large objects, cleaning flash off of castings, grinding welds smooth, etc.
If you do both fabrication and sharpening, you need more than one grinder.
Belt grinders--actually belt sanders for metal--are excellent choices for a lot of the things formerly done on grinders, including sharpening.
Burr-King, Baldor and Kalamazoo are three good choices for belt grinders. The first two are the best, and also the most expensive by far. They're both USA-made. Kalamazoo is cheaper, generally adequate for home or light-duty industrial use, and also made in USA.
Once you've used a brand-name USA-made grinder that is in good condition with quality balanced wheels, you'll never again be satisfied with an Asian import grinder of any sort.
The DeWalt and Porter-Cable grinders previously mentioned are little to no different in quality and operation than most other Chinese made grinders.
AFAIK, Baldor is the only remaining USA maker of conventional bench grinders. They are not cheap. Nor are they as good as they were 20 or 30 or more years ago, but they are the best thing available if you want to buy new.
If you're willing to do a little work to tune up, repair or restore a quality used grinder, there are lots of options available. You may have to willing to spend some time searching for replacement parts or even fabricate them yourself. Even if you don't want to do that, and want to buy new, you may well find yourself doing tune up and modifications to a new grinder to improve the crappy tool rests that most of them come with, and balancing or replacing the even crappier grinding wheels almost all of them come with.
There are many brands of older grinders that can be every bit as good as Baldor when they're restored to proper running condition, and they'll usually cost you far less than an equivalent-sized Baldor. Mainly, you'll have to look for grinders that are 25+ years old to find quality.
Some name brand recommendations for high-quality used grinders:
Black & Decker 6", 8" and 10" grinders made before 1980. These date from the era most young people don't even know existed, when Black & Decker made well-respected industrial tools, but stay away from the small light homeowner-style 5" and 6" models that along with all the rest of B&D's name brand dilution ultimately helped destroy B&D's reputation for quality.
Craftsman 6" and 7" block grinders" made between the early-1950s and the mid-1980s. Craftsman also offered some conventional-style grinders in the 1940s and 1950s that were excellent quality.
Dayton/Grainger brand grinders made before 1980. Make sure they're USA-made.
Delta and Rockwell 6" and 7" grinders made in the USA before 1990. These are arguably every bit as good as or better than any 6" and 7" Baldor ever made.
Doerr 6", 7" and 10" grinders made between 1950 and the mid 1980s. Doerr was originally the "dor" in Baldor (Edwin Ballman and Emil Doerr). Doerr mostly made high-quality grinders for other brands, including Dayton/Grainger, Delta, Rockwell, Milwaukee and others. They're among the best bench grinders ever made in the US.
Stanley 6" and 7" grinders made between the 1930s and late 1970s.
Wissota grinders. Wissota made grinders under their own name and also for many other brands, including Delta, Blue-Point, Snap-On and Milwaukee.
Other good grinder brands, mostly dating before the 1960s:
Atlas, Brown-Brockmeyer, Ex-Cell-O, Millers Falls, Skil, Thor, Walker-Turner.
It's OK. I had this industrial red paint by Balchan. Never heard of it before, never used it before. Took the whole grinder apart, stripped it all down and then this paint was giving me fits. I'm sure the temperature had something to do with it but I've painted plenty of things in similar weather and didn't have a tenth of the frustration this paint gave me. It's really thick and seems pretty rugged so I'll give it that. Still, runs **** and I didn't feel like redoing it all because it's not a grinder brand that a lot of people go looking for. I don't think it will get a lot of bids but it runs like a raped ape and is a really nice USA made grinder.