Gaming is a stress reliever for me and 99% of my game time is still spent in multiplayer. Those who think that you have to interact with others simply because it is multiplayer may need to spend a little more time in multiplayer. Though I get people who just enjoy single player games and want to avoid the stress that comes with multiplayer competition. To be honest there is very little socializing in matchmaking unless you purposely party up with others. I love Halo CE. That was my LAN go-to after spending countless hours with friends on the N64 playing GoldenEye, Smash Bros, and Mario Kart. However, when Xbox live arrived, playing online just blew everything else out or the water.
Playing against new competition every day keeps things fresh. A computer you learn its tricks and play style once and then it's the same thing over and over again. Playing against real people where they are creative, spontaneous, and clever, provides that thirst to come back and keep competing, at least for me. So I was sad when Halo 2 came out because it did away with a lot of LANs, but at the same time I couldn't put down the matchmaking on Xbox live. It was just too good.
So yeah I'd choose multiplayer over single player/LANs any day. Infinite replay value.