Fisherman's Wharf is probably the best choice for first timers. You're smack dab in the middle of one of the biggest tourist areas with plenty to do around town. I was just in a "historic" hotel in Union Bay, and let me tell you... Historic is just another word for "old". Unless you're really into that kind of thing, there's really no benefit to going "historic". The homeless situation around Union Square has also gotten way out of control, although Fisherman's Wharf is only marginally better. Union Square is great, but it's really a shopping and commercial district while FW is a tourism district.

Lastly, two rooms for 6 people... With larger rooms and free breakfast...