I'm also in the Furthur camp by a large margin. To my ears they are by far the most consistently high quality and interesting performers of the Grateful Dead catalog, some new covers and even love a couple of their new songs -- especially Big Bad Blues.
For recent reference, I saw 4 of the '09 Dead shows and enjoyed 2 of them but the other two were very weak and saddening. Fundamentally, I like Warren's sound with the Allmans but not with the Dead.
I will travel to see Furthur as frequently as possible. They are absolutely killing it, are playing a wide variety of material and, frankly, are often performing the music better than the Grateful Dead with Jerry. There, I said it. Nothing's better than the Grateful Dead when Jerry was at his best, but during many periods in the 80s and 90s we all know that wasn't the case.
Enjoy Furthur while you can. We won't have them forever and I, for one, feel very fortunate to have the opportunity to see and hear them. I don't think they're perfect (e.g. would prefer less Phil vocals) but my complaints are minor.