Oh, at the moment. Well, whatever, i'm doing a list of both.
Currently:
1) X to I(what the **** else would be #1?)
2) MC Steven's Extra Cheese Pizza Countdown(as done by the Block Rockin Beats Man)
3) Justin's Dozen Rock Videos Countdown(It's not amazing, but it's got a lot of good songs on it.

)
4) SHADE's Revenge(though there are some songs that seem so off compared to their brethren)
5) Bringing the Rawk(I'm probably one of its biggest critics, but I still think it's alright.)
Trust me, there are plenty of others out there, like "Rafael's Top Ten", "Plus/Minus Ten", "Arith's Urban Advocate"(still the best urban countdown in YTT) and tons of great weekly countdowns(Oasis, Damn Yankee, DJ, etc.) for all of you to enjoy.
Now, all time..
1) The PDC(yes, the name change to The BRC is, in part, an homage to this great countdown. Sue me.)
2) The TC 10(there hasn't really been a weekly countdown quite like it and, believe me, I tried.

)
3) X to I(yes, it's that awesome.)
4) The Omega Connection(people forget about this countdown now, but this was the **** back in the day.)
4) Kworb's Lust Cabin(so weird, but that's part of its charm.)