I can't say yet; we're still working on Council (like every other casual raid in the universe).
I like ToT so far, although I think the tuning is a little too brutal on normal, particularly the ramp up between Jin'rohk and Horridon. But the general design seems cool, and I like big expansive raids. The bosses are neat and judging from LFR have many unique mechanics. Overall, it feels like Blizzard put a lot of effort into it and I'm please on that level.
Ulduar isn't my #1 but it's in my top 5. If ToT keeps up the pace -- and if we actually are able to even clear it at this pace -- it will probably rank pretty high. I couldn't say which would be higher, though.