Most local retailers will advise you to buy as big a screen as will fit in your room and that you can afford. You’d be smart to take that advice so you won’t be back in a year buying a bigger one.
Colors and Resolution
One test of a TV’s picture quality is its “black-level performance.” Generally, those that show the blackest blacks are the best.
Test the remote. Some are more user-friendly than others.
Is the sound sufficient for your needs without hooking it up to an external sound system? Or were you planning to do that?
Don’t pay extra for “bells and whistles” that you think you may never use.