I voted for the Oude Kwaremont. First of all, it's got a nice name. Especially if you try to pronounce the 'mont' french, like Jose de Cauwer always does, with Wuyts constantly trying to correct him. It's uncharacteristically long for a Flemmish climb, over 2 km.
It starts on tarmac, a small road, quite steep already. Then you get the cobbles, quite steep in the beginning untill Kwaremontplein. After that, the climb levels off, but it goes on a long time. Because of the small road and the length of the climb, it's perfect for making decimating a peloton. I like it the most if they do the descend on the big highway afterwards (like in KBK or E3), guarantees fantastic images of all these small groups going all out in the descend.