It depends on the time of day/situation.
Before noon, nothing is more satisfying than a Mimosa, which is orange juice and champagne. They go especially well with pancakes and bacon, and the best part is, they help out with hangovers. Of course, try tailgating at a college football game with one of these, you'll most likely end up being stuffed into a port-o-potty by 3 guys in overalls named Joe-Bob, so be careful.
Late at night, or traveling by airplane or train, it's gin and tonic all the way. It's fairly light, and the citrus taste is quite refreshing. Some have been known to add vodka to their gin and tonic, but it is not highly recommended. Be careful, though, too many of these, and you'll wake up feeling like someone was shoving pine-needles down your throat all night. Not pleasant.
If eating pasta, or I'm out to dinner with my father and he's buying, nothing tops a fine glass of red wine. A good Chianti is hard to beat, especially with pasta, but there are plenty of good California Cabs that do the job nicely. I've never really been a huge Merlot fan. Of course, if I'm buying, I never get wine because most of the good ones are just too damn expensive.
Pretty much any other time, it's beer. I'm a pussy who drinks light beer most of the time for caloric reasons, but I much prefer a good pint of Guiness. My favorite beer, though, is Brooklyn Lager - it's very heavy for a lager, and quite tasty as well. I recently had the intense pleasure of visiting a bar in NYC that had it on tap, and it was out of this world.
So, I guess my answer is that my favorite drink depends on what time it is, where I am, what I'm doing, and what mood I'm in.
