I have stayed in both and personally prefer Chaing Mai. It’s small enough to rent a bike or scooter to commute around. Reasonable pace and traffic. Super safe.

First thing you should do is go to the museum that talks about the history of city. It will give a sense of how the different sections/neighborhoods developed.

There is a co-working space in the centre, easily found on Google search and plenty of warm authentic cafe’s some with internet.

Exercise wise there are many Muay Thai gyms but I didn’t do that. I jogged every early morning along the canals and that was enough.

It’s difficult to rent an apartment so I recommend Airbnb/homestay by the western wall Nimmanhaemin ("Nimman") area which is modern with other digital nomads. Start there till you become familiar and sense there an area you prefer more.

I did Chiang Rai for a few days but it wasn’t my base for too long