First, Blood or Unholy is a preference thing. If you are on the bleeding edge and truly min-maxing, the question would have more value. As it is, it is really just up to you. They are close enough that unless you are getting the FULL potential, you will likely not see a big difference with either.
Blood does use Arp but it is not gemmed until you have enough. ArP is not bad for Unholy but you would not stack it, just take what is on the gear. A link to your toon would be helpful as far as helping you.
As for ArP, please search the site. I hvae posted ArP advice no less than four times in the last month so I know it can be found. Keep in mind, Blood DKs, dps warriors, rogues, MM hunters and feral druids all use ArP so you don't have to restrict yourself to DK threads.