The valve won't turn so I'm looking to replace it.
I think it's a sweat type but I'm looking for confirmation.
Is this a sweat or threaded valve?
It is a sweated valve with a screw on attachment for the toilet connection.
Rather than try to remove it, I'd buy a second one; they are typically quite cheap. With a helper available, use a giant wrench to try and break the valve free. If the valve breaks, turn off the water; if it moves, great.
If it doesn't break free, take the handle off and then take the packing / valve mechanism out by unscrewing the front hex net and removing the valve innards. Replace them with the parts from the donor valve.
If you get lucky, you'll save the time necessary to desolder, clean, and re-solder a valve.
Is this a sweat or threaded valve?
It is difficult to determine if the pipe is galvanized or copper that has been painted silver.
Threaded for the former, sweated for the latter.
I bet on sweated copper as i see a drop of what looks like solder just under the valve on the pipe. Plus i do not see any threads under the valve as you would typically see with galvanized and threaded connections.
Scrape the pipe to see if you can see copper.