Throw all transport modes into one super dense place, and ask which you would most like to be riding. Having a horse would be cool, if it didn't get startled too easily. Plus there's the poo, which was so bad in the 1800s, it even made driving look good.
An off road motor bike would be a great congestion buster, but I worry a greater burden of care would make me reticent about using, or abusing, such power; I'm sure I would be charged for causing a pedestrian the slightest of grazes. That burden of care has already ruled out driving through the most congested places on earth. You have to drive so slowly, to avoid hitting a pedestrian then going to gaol, that it's a waste of your time even trying. Subways are a joke: too much waiting and cramming. So what to ride in super dense places?
Well of course I'm going to say a bike is the tool of choice, when cities get super congested. This is a bike blog, last time I looked. Rather than arguing the case for the bike, watch me ride through Times Square and judge for yourself, if cycling beats walking, beats driving, beats public transport, when the crowd really thickens. I'm filming myself with my iPhione, riding after lunch, on a warm public holiday, when there really are quite a few people around.