Chiang Mai vs. Bangkok for a 3-Month Stay?

Planning my first long trip to Thailand. Torn between Chiang Mai and Bangkok. I like nature and a slightly slower pace (leaning CM), but also enjoy city life and convenience (leaning BKK).

How do they compare for nomad community, cost of living, ease of getting around, food options, and things to do on weekends? Which would you recommend for a first-timer?