South Lake Tahoe
There are exceptions, but this is the basic rule to remember: "South Lake" is a concentrated town of a few square miles, and "North Lake" is more of a general term for the whole north side. If you stay in South Lake, you will be within walking distance of the town's attractions, which include nightlife and dining options outside of those present (or not present) at the hotel. You'll also find a lot of casinos in South Lake, whereas they are few and far between otherwise. Once owned by Frank Sinatra, North Lake's most infamous casino, the Cal Neva Resort, is currently closed for renovations.
If you're looking for a secluded, resort experience, begin your search on the North side of the lake. If it's a smaller, more boutique-y experience that comes with the support of a town, South Lake is where you belong. Both sides have plenty of small inns, so your decision rests on whether or not you want the nightlife.
[Photos: North Lake Tahoe/Facebook and WakeandWander]