We were there for the first time last May and went all over the city via Metro, buses, and Hohos. Rented an apartment in the 10th arrondissement and walked to that famous bakery! We went to both major train stations, and except for a nasty flim-flam man in Gare du Nord, no one threatened us. I would highly recommend visiting Paris if it is on your bucket list.
I LOVE Paris. Bestest city in the world.