It depends on what you're going to do with it.

If you want a great picture at a low price, and space isn't an issue, get a 21" flat screen CRT.

If you want it to look "Cool" then get an LCD.

If space is at a premium, get an LCD.

If you want to be able to rotate the screen and work in portrait mode, get an LCD (but not an Apple one)

I use a 22" Trinitron CRT, but I have a huge desk. It runs at 1600x1200@85Hz with no problems.