Led monitors are in actually LCD monitors with LED backlights instead of LCD monitors with Florescent backlights.

The advantages LED have over LCD is this
*Uses Less Energy
*Thinner
*Cheaper to manufacture (note I didn't say cheaper to buy, but it is cheaper to manufacture for the vendors)

LED can sometimes have better color than LCD, note I said the word sometimes. The only thing different between LED and LCD is the lightbulb used you are trading big for small and uses more heat for less heat. The only LED tvs with truely better picture use RGB Leds instead of White LED and are capable of local dimming but you won't find these features except in the very high end tvs because the make the cost to manufacture much more expensive.

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120 hz is much more important. The reason why 120 hz is more important is that it makes film look smooth. Film as in movies are filmed in 24 hz, TV is filmed in 30hz. If you play movies in a 60 hz tv then you are doing something called the 3:2 pull down. The film shows some frames 50% longer than it should to obtain the 60 hz.

With a 120 hz tv it can operate at 24 hz, 30 hz, or 60 hz without any frame taking longer than it should. Now some tvs have little computer chips built inside of them that analyze the 24 frames of video a second and extrapolate what movement occurs between frame 1 and frame 2 and instead of showing frame 1 5 times followed by frame 2 times tries to create a frame 1a, 1b, 1c, 1d, 1e. Sometimes this computer chip makes the picture look better sometimes it makes it look much worse. Most tvs allow you to turn this feature off.