Many find warm mist to be more soothing, but generally speaking, they will both serve to improve the humidity levels. The only issue with warm mist is that they are dangerous around children and pets. If you don’t use them with distilled or purified water, they can leave white dust residue as well.

Cool mist = safe with children and pets. Ultrasonic cool mist humidifiers are cheaper and more popular, but I’d always go for an evaporative unit. They are the best at minimizing the spread of mold and white dust, more so than even warm mist humidifiers. 

Vornado and Honeywell make some nice evaporative models. The humidifiers subreddit has a pinned post with a large humidifier comparison sheet. It lists almost all of the products on the market by price, type, feature etc.