What faction should I be grinding with a brand new 80 paly, spec. is Ret and Holy, but Im more interested in the Ret gear. I am wearing mostly greens still due to just doing quests to try to level as fast as possible.
For ret you want the Ebon Blade for the AP/Crit head enchant
For holy you want the Kirin Tor or Wyrmrest Accord for the SP head enchants
http://www.wowhead.com/?item=44159 - Has crit (preferred)
http://www.wowhead.com/?item=44152 - Has MP5
I would recommend aiming for the enchants, as these are the best currently available, and once you start running instances you should rapidly start replacing gear.
Once you start running heroics regularly, which you'll likely be doing pretty soon, you'll be replacing any faction gear, with the possible exception of the Death Inured Sabatons (http://www.wowhead.com/?item=44306), which are from Ebon Blade exalted anyway.
Go to Gear Wishlist. The site is kept up to date as much as possible, and it allows you to put in your character, and pull up a list of his current equipment, and then list all the items that are of that same slot, ranked from highest upgrade on down. It allows you to mouse over the gear in question and see what the stats are compared to what you're wearing. Best of all, in my opinon, is that it allows you to sort/filter for terms....such as Vendor, or Emblem, so that you can see what gear you can purchase.
As others have pointed out, you'll want Ebon Blade for Arcanum of Torment and Kirin Tor for Arcanum of Burning Mysteries (or Wyrmrest Accord for Arcanum of Blissful Mending, but crit is better than Mp5).
As long as you're not a Scribe, you'll need the Sons of Hodir for any or all of the shoulder enchants.
After that, pretty much all of the factions have something to offer, especially if you have greens to replace. I would recommend Ebon Blade again for the Death-Inured Sabatons because those things are just awesome. Each faction, however, has a little bit for every role.