Is it easier to drive to North Lake Tahoe to ski when coming from SF, rather than going to South Lake Tahoe? And how easy is it to get from north to the south after skiing?

As others have said, driving to either from the Bay is about equal in good weather, but easier on 80 to North Shore in bad weather.  In good weather, it's a little over an hour from north to south, can be 2 hours in the snow. I recently did San Jose > Squaw > Kirkwood in bad weather.  80 under chain control you can expect to go 30 mph for the last 40 miles to 89 or 267 to get to N Shore.  However, being wider than 50 makes this much less difficult.  Going north to south people generally prefer the east side of the lake, on 28 > 50.  This took 2+ hours under chain control for me (Squaw to a motel), largely due to traffic going through King's Beach and Incline Village.

Yes it is generally easier to get to North Lake from San Francisco than South Lake.  This is because you take I-80 all the way to North Lake but need to switch to the US-50 to get to South Lake.  The 80 being a federal interestate has more lanes and is generally less affected by storms. It takes about 1 hour 15 minutes to get from Heavenly to Squaw Valley with good conditions and traffic.