I run LEDs, two Hydra 52's.
From what I've gathered when I looked into it a few years ago...
Some pros:
LED bulbs last a lot longer, so maintenance costs are lower.
They also produce less heat.
They also are lower wattage so your electric bill is lower.
Some cons:
The up front cost is a little more, good LED's can be pricey.
There is a range of quality in LEDs, so you can get poor results with poor LEDs.