It's amusing to see people arguing about ancient history. The competition for server firsts certainly did add some excitement to the raiding grind, but it also engendered a lot of misplaced anxiety (e.g., about each other's raiding schedules). =P
Anyway, Ascendent was first on C'Thun. In fact, I think it was pretty close to a world ranked kill. Then I joined the guild, and everything went downhill! Naxx is a bit of a blur, probably because of Blizzard's borked release schedule.
After that, my recollection is that Ascendent's server firsts were... one of the lame bosses in TK (pretty sure it was Void Reaver), Archimonde, the orc in BT that you 3 tanked, Gorefiend, and best of all, pre-nerf Nightbane (suck it, Blue team)
I seem to remember most of SSC being a fiasco for us, even though it did produce one of my fondest WoW memories (the Bilmo u-turn on Hydross and subsequent meltdown). BT was actually going well up until RoS / Christmas break. We had a couple of raiders quit around then (Tsegoa, Oku, maybe Nics too), and it took us a while to get going again. On Illidan, we had some tanking issues, and we definitely weren't first there.