Basically, the common rule (altho this is only at the moment and technology is moving so quick) is that 42 inches or over, plasma is better and below, LCD is better. However, this is down to peoples opinion (so dont shout at me!). If you are spending �1200, you could get many models that would suffice, but I would suggest making sure that it's HD ready.
Also, regarding brands/models, most major brands shouldnt be a problem just steer clear of unknown makes.
Try buying what hifi and reading the reviews 1st as this will help a great deal
Good luck!