a couple things in my opinion. first, contrast ratio, the higher the better the picture will look from white to black. second, refresh rate, the higher the better. with a high refresh rate like 120hz the action is smother and not choppy. finally, resolution, 1080p (progressive) is the highest but if the signal you are putting through it is of a lesser resolution the picture degrades if the tv does not have up-conversion technology. example is regular definition tv which is about 480i (interlaced) may look worse on a higher definition tv without the upconversion as opposed to a 720p hd tv which is closer to the actual resolution. if you are not shelling out for a blue ray player and are just watching dvd's and hd tv then 720p may be your route. if you got blue ray and all hd channels then 1080 may be ur route. if u want the top of the line then 1080. also the best picture now is from LED tv's. they dont burn in pictures like plasma, they dont burn out in 5 years like plasma, they offer better contrast/refresh rate than lcd, and over all they are brighter. for instance u can get a 55" 240hz 1080p LED tv for around $3k. Smaller sizes cost less. Also consider the new stuff, 3D ready. These are cool but more expensive due to glasses r needed, adapters, emitters, and over all accessory overload. Lcd is most affordable, dlp is thicker tv set dimensions, plasmas are expensive and have issues, led is the best in my opinion.
Oh, also i saw a 40" samsung LED 120hz 1080p tv for $999 on newegg.com with $19.99 shipping.
Just for comparison. I got my dad a samsung and he is thrilled with it. I am thinking of getting this one I just mentioned. Excellent picture. Oh and in lcd's bigger screen try to get higher refresh rate. Hope this helps