Depends where you're going. There is no bus that goes to my current office, but biking is slower than driving because there is no significant traffic (7 minutes by car, 20 by bike + changing).

My last job was 45 minutes by car or 20 walking + 30 bus1 + 10 waiting + 15 bus2, but then you have to take out -20 exercise (walking) and -30 sleeping (bus1), so I usually took the bus. And bus2 was actually a lot of fun... There were a bunch of women who spent the whole time gossipping, it was fun listening to them . The bus was more reliable than driving because it took the HOV lane and the regular traffic lanes would sometimes back up enough to easily double the driving time. That route was 23 miles by car but almost all of that was interstate, the bike route would have been probably 5 miles longer at least since I'd have to find smaller roads to take. At the time I didn't bike to work however so I don't have a good comparison.