San Francisco International is much easier for Immigration and Customs / Customs and Border Protection at any time of day; the officers are pretty reasonable and welcoming. Los Angeles International can get very crowded at times and harried officers in Customs can end up shouting at arriving passengers like they are driving cattle.

SFO the terminals are easily accessed via an elevated tram that connects the terminals, and connects to the BART (light rail) system to San Francisco proper, as well as connections to trains to San Jose, etc.

LAX one often arrives in the Tom Bradley International terminal and must exit the terminal, and walk (ground level in inclement weather, open air on second level in nice weather) or take shuttle busses to other terminals or to other transport. Some issues are affected by which terminal one arrives and departs.

LAX has more connecting flights, and has two runway pairs with standard separation, and is rarely affected by inclement weather. It also offers a greater variety of flights if one's connection is hit by irregular operations (ORD readily comes to mind).

SFO has fewer connecting flights, can be affected by other airports' problems with ground control holds and has two runway pairs with non-standard separation - they must close one runway of each runway pair during any inclement weather, such as rain , fog (SFO can get fog in summer), etc.

To echo others, it depends where you are going on to, to a large extent.