The Executive Lounge in the Prague Hilton is one of the best I've experienced. The food and drinks are wonderful, and the lounge staff are exceptional. Although th Prague Hilton is a bit further from town than the Hilton Old Town, I think it's well worth it particularly if you're going to be using taxis anyway. Unfortunately, I haven't been to Vienna (but it's high on my list of places to visit!). Enjoy your time in Prague. It's a fantastic city!