Unless you have no other option (ex mounting on top of fireplace) the
TV should be at eye level. I have my 42" mounted on the wall opposite
our sofa at eye level when we are sitting on the sofa, witha small 20"
high entertainment table on the bottom for the cable box,DVD etc. I
used a fixed wall mount since it sits closer to the wall. The optimum
viewing angle is directly center in front of the TV.
If you must mount higher than eye level, use a tilt-mount so you can
tilt the TV down.