NCL offers Freestyle Dining: you can dine when you like and with whom you like in single, open seating. The newer ships, built in 2000 and later) have up to ten restaurants to choose from. Three have a surcharge, the others are all free.
Princess has something similar. You can choose between standard assigned, two seating dining OR, you can opt for single open seating (there are two restaurants). In addition there are two alternative dining restaurants (surcharge) and the Lido buffet is open 24 hours per day.
the largest tables i have seen are for 10. I am not quite sure what you mean by banquet style seating. You can request any size table that you want on any cruise line regardless if they have traditional dining or a flexible option.