We did them in order and none of them really stood out as particularly challenging (relatively speaking). It also helped that we had a disc priest, 2 paladins (prot and holy), and a warrior OS tank, as well as good slime handlers (hunter, ele sham, destro lock). If you have a good setup, it's probably just as difficult/easy as any other bosses in the first 8.
At this point I don't really see a reason not to do them in order, in case you get a kill early in the week so you have a shot at another.