We enjoy both. If I have a preference, I'd say it was for Tusker House. However, because you say you're going to have one of the last reservations of the evening, I'd personally be hesitent to book a buffet. It would make me feel rushed, and I'd be afraid that they wouldn't be re-stocking everything the same they would earlier.
We actually ate at Tusker near closing on a trip several years ago. The only two things I specifically remember was that the bread on the buffet was a little stale, and that it was difficult to get our server's attention for drink refills because he was busy cleaning and stacking chairs in another section of the restaurant. I must say that I can't remember any of the food items being out of stock, though, so I guess they do keep cooking until everyone is done.
On any of the half-dozen times we'd been to Tusker for lunch, I'd never had a single complaint.