I have both and love both (1 bubba keg, 4 bge's). The keg is more efficient, but just barely. The keg can be touched when it's 700, but give it 10-15 minutes and that touching stops. I have measured my keg at 400 on the outside with an IR gun when doing pizza. That's the same external temp as an egg at that temp. The egg is easier to cook on. Can the keg do what the egg can, I think so. The egg is just easier to do it with because of the thermal mass. If you forced me to pick one, it would be green. But I do like the portability of my keg, that's really the reason I bought it.
John - Salt Lake City, UT