Make sure the tv is 1080p. The size really depends on the distance from the tv that you will be sitting. Where LCD/Plasma/Projection comes into play is the contrast ratio mainly and also weight. TVs with a high contrast ratio like 10,000:1 will have a truer black than something with 1,000:1. In terms of weight: Rear Projection > Plasma > LCD > LED.
Depending on your cost, name brands will produce the best picture. Most important make sure the tv is 1080p with a high contrast ration and also with a minimum of 120hz. These details will give you a true HD accompanied with your cable or satellite provided HD.