I vote DDO, but I have a nostalgic love of AC as well. Due to being an angry purist Tolkien fan (the kind that insists on watching the extended edition movies and then complains all the way through), I probably won't be trying LOTRO.
As much as I loved AC, DDO's graphics are richer, and I enjoy the instanced dungeons and the fact that I was actually able to cap a couple of characters, whereas my husband and I had hit a terrible grind in AC before we switched games. I miss my cottage, though, and the randomized loot.