This is quite a tough choice. MDMA is the only drug I really can't imagine being worth it alone, and it is probably the most fun you can have on a Friday night with the right people, but the fact that you have to space it out so much and find friends who want to roll makes it hard to fit into normal social situations, whereas alcohol is universal and can be enjoyed several times a week without as much ill effect (assuming a certain level of moderation and consumption of water).
And I love tripping with people a lot, or just drinking coffee and smoking cigarettes with people. Most drugs I do I treat as social drugs, except salvia, which I still do with people for safety reasons.
I think as far as really connecting with people, particularly good friends, MDMA, and as far as easing normal social situations, alcohol. And both are better when combined with coffee and cigarettes.