+4 3/day. We don't have enough encounters per day in this current adventure to make anything more than that, considering that 1-2 encounters is currently all our group can handle in a single day under our current DM.
It really depends on the rest of my character. If he already has a decent damage output, I'd go with one of the first two choices. If he's somehow lacking in damage, I'd go with the later ones.
I liked +12 once per day. That would make it an extra-special ability that the character would save for an extra-special situation, which would make it more exciting (for me at least).