Rate 1-10 in:
Battery Life:
Speed:
Performance:
Looks:
Features:
Battery life is the same in all three, it's your use and apps that make a difference, not the rom. Remember, all use a similar kernel and processor. Bumblebee may have a minimal edge here due to the T.W.O. fix, but that depends on where you live and how badly you are affected. Some will see no change, others claim to see a big change. Harmonia was built on Aphrodite, which was shown to be quite good on battery though.
Speed, all should again be pretty similar really, but Bumblebee probably has a very slim edge at certain things, like sdcard speeds. Same as before, they all use a similar kernel and processor. BB just has a few more tweaks.
Performance, isn't this just speed?
Looks, while subjective, Harmonia both wins and ties for a loss here. It technically has no looks, but offers the most options for it. What it doesn't provide, you do yourself. Reborn probably wins as it has a different launcher.
Features, Harmonia loses here because it is a stripped down rom. You add the features you want. Reborn probably wins here.
Two things not mentioned are
stability and compatibility.
Of them Harmonia is
probably the best since it is as close to stock as possible.
As mentioned, try them all.