Edur, of Gorgonnash-A (EU), has created a web site that relies on game data form participants to rank the realms according to their completion of the Sunwell questline, and a very nice site it is. You can see all the US and European realms and where they stand both on the main phase quests and on the side accomplishments, like constructing the portal from Shattrath to Quel'Danas. There are also nice progress charts for each individual realm, and, most usefully, ETAs for when the objectives might be reached given current rates of completion.
Currently leading the pack is Proudmore (US), with 44% completion of phase two and 75% completion of the portal. My own realm has jumped up from about 40 to 25 in the past few hours -- go Shadow Council! Five US realms are show as still languishing in phase one, although Nordrassil was at 98% as of the last update a few hours ago, and has likely moved on to phase two by now.
On the European side of things, the German realms are in front, headed by Gilneas at 30% through phase two and 55% complete with the portal. Since they're a day behind (they receive patches on Wednesdays, whereas the US gets them on Tuesdays), it's not surprising to see them a bit less progressed.
If you want to help out, download the AddOn from the site, and then be sure to upload your data file for analysis. And if want to use this data for some nifty site or service, the site's author has helpfully made XML feeds available under a Creative Commons BY-NC-SA license. Well done, sir.