I have an old round column Grizzly mill -drill. It's around 20 years old now and still going strong. The round column is a bit of a nuisance , mostly because it won't take heavy cuts - anything over .035 is a heavy cut on this mill- without often digging the cutter into the work and swiveling the head around , ruining the setup and sometimes the part. I've found this is a more prevalent problem than needing to raise or lower the head, ruining tram. But overall they are a good learning machine.
I think Grizzly dropped the round mill design a few years ago in favor of a square column.
The other issue with larger mills, is many need 220-240 volts, either single phase or three phase. So assess what your existing shop electric service is currently, and watch for a mill that fits within your power supply.