Well, only you can decide what size and type is best for you. Generally though, it is hard to use a TV as a PC monitor(for long periods at least) as it just isn't ergonomic(unless you are doing non-PC exclusive tasks like watching videos or playing games). You also have to decide what is in your budget.
Technically speaking all LCD TVs are monitors and function practically identical to their small format brothers. It is mostly down to cost and use. 21" is considerably small if you are planning on sitting 4'+ feet away, but 32" is way too big if you are going to sit 2'- away. Oversized monitors cause eye strain because you either sit too close and it causes too much movement to take in everything or you sit too far back and you are unable to easily read/navigate. PC interfaces just aren't designed for sitting way back from a big screen. However, video game interfaces aren't designed for sitting really close. It is, however, easier to use a game console on a smaller screen then a PC on a bigger screen.
Technically speaking all LCD TVs are monitors and function practically identical to their small format brothers. It is mostly down to cost and use. 21" is considerably small if you are planning on sitting 4'+ feet away, but 32" is way too big if you are going to sit 2'- away. Oversized monitors cause eye strain because you either sit too close and it causes too much movement to take in everything or you sit too far back and you are unable to easily read/navigate. PC interfaces just aren't designed for sitting way back from a big screen. However, video game interfaces aren't designed for sitting really close. It is, however, easier to use a game console on a smaller screen then a PC on a bigger screen.