Most air travel within Thailand has Bangkok serving as a hub. Depending on the distance, and especially if you are already located in Bangkok, air may be the way to go. A long trip to convenient airports, such as Bangkok to Chiang Mai, Chiang Rai, Phuket, Kon Kaen etc. is best done by air.
If you are starting from another place, such as Nang Rong, it gets more complicated. For example, Chiang Mai is about twelve hours from Nang Rong by bus. To go by air you must travel five hours by bus to the airport. You will probably need to get to the airport in plenty of time, so figure more than two hours there – probably more like four or five because of schedule matching. Then you have the one hour flight to Chiang Mai. You may or may not actually save time. Maybe it is better to just get on a bus. Perhaps going to Korat and getting on a plane to Bangkok and then to Chiang Mai would be better. No volunteer here has looked into that.