BC is first for a lot of reasons it is when I started raiding then eventually raid leading and I managed to see each raid and all but SWP to completion prior to Wrath.
Wrath had it's share of pitfalls for sure, but I did enjoy all the raids besides RS. Sure ICC didn't need to be 12 months of what it was or gated the way it was but it still was fun for a good chunk of that time, even if the first 4 bosses seemed like punishment while you were racing past them week to week.
Cata was fun to start and slowly got worse as the expansion pushed on. I am not going to hate on DS the same way most seem to, but between it's rapid nerfing and the amount of time it was out it was turned into a steaming pile by Blizzard.
MoP maybe the next tier or raids will be mind blowing who knows. HoF is the worst raid so far as far as it goes for me, not much fun and busy work and mechanics for the sake of doing it. MSV was ok at best and with Terrace it wasn't bad but not enough to salvage the tier from the other 2. ToT isn't much better then the others so while putting an incomplete expansion last is some what poor form last is where it goes for now.