The public transportation in London is extremely efficient. Wherever you are trying to go, you have three options of how to get there: the bus, a cab, or the tube. The bus is good for going places that are just slightly too far to walk, and the tube, one of the most iconic things about London, works for everything else. The tube is clean, speedy, and can be easily understood by even the least savvy tourist. The public announcements on the tube are very clear, and riders always know when one of the lines has delays (which unfortunately happens quite frequently). Also, the names of the tube stations are arguably the most charming thing about London.
Although cabs are fun to take and very comfortable, they are far too expensive to use on a regular basis. If you find yourself far from home after midnight (when the tube closes), however, you sometimes have no choice. The high price of cabs is arguably well spent because you will never find anyone more knowledgeable about the streets of the city than a London cabby.