If your talking response time smaller screen have less response time and so are "faster" at transmitting data from the console to the screen. aka less controller lag. So in that sense it's better. When I go hardcore I use a monitor (Even faster). But when it's just casual I switch to the big screen. :)

I'm going to say it probably comes down to price and space... they aren't going to fork out the money for 50" + T.V's for every contestant. It would also take up a lot more space doing so. At home, the same applies. They might even make a conscious choice to play on a smaller T.V to 'train' on what they use in competition. For the average gamer though, it all comes down to how much you can spend and how far away you will be from your T.V. The further you are away, the bigger you want to go. I have a 46" LED and sit around 1.5 - 2m away. It feels perfect for me and I have no issues with 'eye movements'. I have no trouble keeping tabs on everything in the HUD and what is in front of me.

in my opinion, anything between 19 and 24" is the best. I think the smaller screens have better gameplay because of less eye movements. [spoiler]Also, If you're an XBOX360 to PS4 Transitioner, read this: http://www.bungie.net/en/Forum/Post/67454104[/spoiler]