What is the fastest way to move upward?

Solution 1:

Hopping with vertically aligned boats or minecarts.

Solution 2:

The fastest way to travel upwards is on an upward slope of powered minecart rails.

Update

Tell a lie, there's actually a faster way, our good friend TNT. Use this at your own risk!

Solution 3:

Pistons elevators are the fastest way to go in 1.7.3 and above.

I believe minecarts would still be the fastest, provided that you have enough space and resources for them.

Stairs would probably be faster than ladders, but again require more space.

Boat elevators and water ladders are now fixed entirely. They will not work.

Ladders are pretty decent. Slow-ish, but efficient.

If you had a fast PC, you may be able to fiddle with portals and see if you can get them working such that you enter portal B at the bottom, arrive in the Nether, get back in the portal, and come out in portal A at the top. For long distances, this is probably pretty fast..if a little unorthodox.