When I first started taking the Metro in Paris, I was really nervous. At the time, my French wasn't very good. I was scared I would miss an announcement or accidentally skip my stop and get lost. The Metro is definitely a little harder to navigate compared to the bus system. The buses also run less frequently than the Metro. For example, the Metro comes every 2-3 minutes, and the longest I think I had to wait for a Metro was 10 minutes. However, the buses run a little less frequently, sometimes every 15 minutes.
I prefer taking the buses because I can look out the window to see and discover different parts of Paris. This kind of sightseeing while I travel isn't possible while riding the Metro because Metro trains are routed underground. I take the Metro when I am in a rush, or have plans, and want to quickly arrive at my destination. If I am not in such a hurry and want to enjoy the environment outside, I will take the bus. It is nice to have these options, especially since I do not own a car!