Yes, really depends on how much time and energy you want to dedicate to each.
The Northern California areas are generally more scenic. Namely the pacific coast highway, up to the San Francisco Bay area. LA has 2 big draws for a lot of people, the outlet malls and Disneyland.
Further north, there's Monterrey, Sequoia and Yosemite National Parks. Napa is great if you enjoy the country roads and visiting the wineries. A little further north of Napa, there's Tahoe.
There are day tours to the national parks from SF and LA, and lots of Grand Canyon tours from LV. But generally, for Yosemite and Grand Canyon, they are best viewed and enjoyed early mornings or late afternoons when the sun is not directly overhead and super glaring (not necessarily hot unless you get hit with a heatwave or peak summer).
SF and the Bay area has plenty to offer, and in the city and within a 5-10 mile radius, generally, the more popular tourist areas can all be accessed by public transport. The bus system there is pretty good and if you have a data roaming service, can access their arrival timings, which are really good in accuracy. So, you don't really need to drive there most of the time. And parking within SF is really expensive. Some of the 'motor inns' do have free parking for guests though many can be quite crappy in terms of room quality. You can take the BART (their MRT) all the way from SFO to the city itself. About US$8 or so. Pretty fast too, about 40mins in peak traffic.
Gilroy outlets are pretty far off from the city, and not really better than the ones you can find in LV.
Actually, LV itself has 3 factory outlets. One to the North and one to the South of the Vegas Strip. There's the Primm outlets which is 5-10mins out from the city which can also the assessed by public transport by taking a bus outside MGM Grand heading east. The over and above the Fashion Mall and so called outlets.
In LV, same thing, basically everything revolves either around the Strip or Old Town. Both are accessible via their bus service. If you're there for a few days, get multi-day tickets for The Deuce. It transits on a North-south-North route of the city and you can hop on and off at all its designated bus stops which are near all the major attractions. Saves a lot of pain of the traffic snarl at times and walking when its really, really hot ( think 40 degrees C in peak summer ! )
It is possible to cover all 3 cities in 2 weeks. You just need about 4 days (max) for LV and Grand Canyon or you'll get bored. Unless you've got a ton of money to burn that is ... :sweat:
Suggested would be to fly in to SFO, enjoy the city and surrounding areas for a few days. Drive over to LA and visit the National Parks along the way, hit LA, and spend a few days there for Disneyland and maybe a bit of shopping. Drive back to SF via the pacific coast, and enjoy the scenery. Fly over to LV and fly out back to SF and back to SG. (Rental cars can be returned in different cities for a small fee)
You could of course chose to drive via the pacific coast and skip driving to the national parks as you can join the local tours to visit them. Instead fly over to LV via LA and fly back out to SF to return to SG.
That way, you can minimise your driving and still have a good trip. Also, you can leave your shopping for LV mostly so that you won't lug so much stuff around with you.
Just some suggestions based on my travels in the US west coast to date.
