Huckabee would be a less electable candidate. He takes a number of positions which, although theologically sound, would prove ruinous. He also comes across as a bit of a yokel.
Romney, on the other hand, is a skilled chameleon of a politician, who says whatever people want to hear, and appears respectable and dignified.
Romney would be a good candidate regardless of what should happen in these next few years. Huckabee will only be competitive if Obama continues along his chosen path to perdition.