If your a student or of student age, then Walkabout without a shadow of a doubt.
Tiger Tiger also has a student night on a thursday, but it's not as good as the monday one from what i have heard.
The only thing to bare in mind is what time your show finishes? Walkabout tends to have a rather large que by 10:30-11pm. It may be worth going down to Walkabout about 5 to get Que Jump tickets as we often do, and it is very much worth it.
It holds about 2000 people and is one of the most consistently busy nights with pretty good drinks deals.