Nice hotel in a good location
I stayed at Hilton Union Square over Labor day weekend, in a room on the 16th floor in Tower 3 facing the pool. The room was recently renovated and was very nice. There is a skybridge connecting towers 1 and 3 with a view of the city. There are lots of seating areas in the lobby and many people hang out their on their laptops to avoid the Internet charge. The hot tub is a great way to unwind after a day of seeing the city and there is also a heated pool. Seems strange there is very little light in the pool area at night.
Hotel is one of those big, convention hotels and can be crowded. It is in the middle of the heart of downtown San Francisco. The hotel is close to some sketchy areas but as long as you go east when leaving the hotel you will avoid them.