Getting around in Nepal is an experience, no matter what form of transportation you decide on.
For the simple routes (e.g. airport) a taxi is your easiest solution. Just remember to always, always bargain! Meters do not exist within Nepal. You will need to set the price in advance.
If you want to travel like a local and get the true feel for Nepal, be sure to hop on the local bus. There will be much hooting and hollering as they continue to shout the final destination out of the door throughout the ride. One hit on the side of the bus means slow down, while two pounds means gas. Be aware that the route will be anything but direct. Besides transporting people, goods will also be loaded onto the roof. And there are never enough people on the bus — even if all the seats and isle are filled. After all, there is always the more room on the roof! Besides loading and unloading goods and attempting to get more passengers, the longer bus rides have a tea and Dahl baht break.
If you prefer a more direct route and your luggage safely bellow the bus instead of strapped to the roof in some sketchy manor, you can pay a little more for the tourist bus. Expect assigned seats and a stop at an overpriced tourist lunch spot. Air conditioning depends on how much you want to pay for your ticket. This ride will be much quieter then the local bus, less time, and very convenient.
If you are heading to Jomsome, Pokhara, or Lukla you can take a domestic flight. Expect a small hopper-plane that seats approximately twelve people. The flight itself is easy, though the airports tend to be a chaotic mess. Especially if you are flying to Lukla, be aware to delays due to weather. You also must be adamant about your ticket. Just because it says a certain time does not mean that’s your flight — or so they seem to think.
All transportation tickets are sold at an escalated price to tourist as a way to subsidize locals’ transportation. Always try to be flexible and patience (and adamant when necessary). Nepal is a lesson in Confusions’ patience.