Both hotels are excellent. The Hilton on the Buda side has a free shuttle from the airport and back, which could save some money for you. This hotel has more character of the two, and has stunning views of the river and parliament.
The West End Hilton is more convenient for getting around and for shopping, its adjacent to a mall, and is just about a block from the train/subway station. Both hotels have excellent service, both have great lounges, althought the nod might go to the West End because their evening spread is virtually a dinner. Both hotels treated us like royalty as Diamond VIP's. You really can't go wrong with either one.