Re: Best site for USA hotels? Recommendations for hotels in San Francisco and Las Ve
Re San Fran, if it's your first visit I'd aim to stay somewhere in Fishersman Wharf which is v close to everything touristy, and cable cars run from there to Union Square/Chinatown etc. There are lots of the usual chains in Fisherman's Wharf area, Holiday Inn, Marriott etc, but if you want luxury then The Fairmont is the best you'll get.
Re Vegas, depending on budget - Excalibur (v reasonable) Luxor (mid-range) but again for proper luxury can't beat the Bellagio which is more mid-strip.
Have a great trip, two fab cities and perfect to do together!