Since we found taxis in Paris to be rare birds - we spent plenty of time both on the Metro and on buses. Each has its advantages/disadvantages. Apart from the obvious (under the ground versus out in the sun) - I would say it is easy to navigate the Metro if you know how to read a map - but it's good to have specific advice about bus routes in advance if you plan to use them (we got our information about them from the hotel concierge). Robyn