Trivago/Lastminute.com is your friend. Unfortunately America doesn’t really do affordable accommodation that isn’t riddled with meth addicts and bed-bugs. It’s basically a choice of that or about ~$200 per night minimum. That’s just the US for you.
The times I’ve spent in SF I’ve stayed right by Embarcadero (which is the lower part of the city but still central) in a couple of hotels which I got deals for on Trivago. Just doing a quick search now and I see most of the results for SF bring you to Union Square area which is really the centre of everything and close to Chinatown, Nob Hill, Financial District, Mid-Market, etc. Embarcadero is down a bit from here, so less central, but I like it as it’s near the water and it’s fun to stroll along the pier in the morning and get breakfast watching the bay. The transport is inferior in every way to London, so there’s no best place to stay in terms of public transport.
If you don’t have Citymapper, I’d recommend installing that for knowledge of the bus routes. If you don’t know your way, getting to places like Haight Ashbury and Golden Gate Park can be tiring due to the hills - especially if you’ve limited time.
I’d avoid Ghiradelli Square/Fisherman’s Wharf. Totally shite and nothing to do.
Short answer: Almost guaranteed that your hotel will be based near Union Square. If you’re going with children I’d probably avoid the Tenderloin which isn’t too far away. In case you didn’t know it’s one of the largest drug/prostitution markets in the US. It’s fine by day (sort of), but at night is pretty gnarly and the real deal in terms of all the stereotypical ghetto stuff you see in the films.
Chinatown is definitely to be experienced though. Don’t be afraid to just wander into the stores and check out all the crazy stuff for sale.
The thing about American cities is there really isn’t too much to do in terms of tangible activities when you compare them with major European cities. However, that’s not to say they’re not enjoyable or interesting. I just find them fascinating to walk around in and shoot photos.
LA: Is enormous. I’m not as qualified to answer this. I know some people have been recently and obviously if Blosrock still posted he could hook you up. I’ve been to LA twice and had some fun experiences. One thing that surprises me still is just how close you are to hiking in mountains/desert. I love hiking and spent a lot of time there hiking around Hollywood and Malibu in the trails which really do have bears and rattlesnakes.
I stayed a few blocks up from Venice beach which I think is probably a good base for doing things, though it really depends on what you want to do. Going everywhere in LA takes fucking forever, so you best be sure you have a plan for where you’re going each day.
If it’s your first time I can’t help but recommend renting a bike or pushing on your board all the way up the beach-front from Santa Monica to Venice to see all the classic spots from the 90s.
When I was there I also rented a bike on the beach and cycled all the way from Venice Beach up to Malibu. Bring some food and drinks with you and some swimming wear.
El Matador beach was really beautiful. As was Zuma beach.
The Getty Center is really interesting and well worth a visit if you’re into art, history, design, etc.
As for food. I just pretty much eat American-Mexican in California. Fish tacos/carnitas are sort of hard to beat…
I’m not going to say don’t go to LA, but if you had more time and wanted to drive and have a little adventure you could do worse than drive up/down to Santa Barbara. The skatepark on the beach there might just be the most perfect skatepark and the town itself has some really gorgeous historical buildings to see. Everything can be seen by foot, and you don’t have the pollution and insanity of LA.