IPB and vBulletin skins outnumber Xenforo by 100 to 1. Please do your research.You can find lots of xenforo great themes here XenForo themes and skins! | Audentio Design, and xenforo for now its best for forum script.
lol lots of IPB and Vbulletin themes are outdated, and need to be fixed to 3.4.6 version like i said before run both script and Xenforo its better and more friendly for user and admins to.