It really depends... If your have the proper source and the right cables its still going to give you a great picture. But it also depends on how far away your sitting from your TV. For a TV that size and if your sitting about 7 feet away its very hard to the human eye to see a great difference between 720p and 1080p. In terms of contrast... alot of companies put there contrast up in bold print and wear it as if it were a badge of honor but its almost a useless number (in terms of TVs) because theres no set industry standard for measuring contrast. I would say trust your eyes, do more research, and trust your gut.
Not to bring Sharp down because I use to be a pretty big Sharp fan but lately I'm just not that impressed with there LCDs. I hate how there pixels are aligned almost in a zigzag pattern. From far away you can still see it if your know what to look for but if your planning on sitting fairly close it would just drive me nuts.
My picks are always Sony and Samsung.