It depends entirely where you want to go and what you want to do.
The last time I visited Paris was meeting 2 friends and their teen DD’s and their skinflint DF wanted us to walk everywhere from morning until night! But you can walk from area to area - I think we did Arc de Triomphe, champs-elysees, Tuilieries and Louvre and a Marais walking tour.
The only time we did a metro was visiting Cluny/La Sorbonne and I got the metro in the mornings to meet them as I was in a hotel near the Eiffel Tower.
New York I’ve easily walked around various areas in a day but you need rest stops and as it’s humid and can be hot, to take your time.
London - I live in London. Ideal walking tours are the Southbank one where you can go to Tate Modern and then cross to St Paul’s etc.
re the above, yes I’ve done tour buses, tour river boats and public transport too.
Barcelona as I was with a family member who’s a paraplegic in an electric wheelchair we used the metro a fair bit bit to get to eg Parc Guell/Montjuïc the buses are fine. But we walked a lot around the gothic, maritime, university etc quarters.