The AM shifters are definitely the way to go if you want off the shelf functionality. However, if you are just building a practice robot or something, you might want to go cheaper and upgrade the system later (AM toughboxes or equivalent), to save money for the build. Look at the whole line of shifters before deciding on anything, the older shifters have some differences.
Dewalt transmissions are also used often, though they take some work to implement.
http://www.chiefdelphi.com/media/papers/1592
As much fun as custom is, I would suggest focusing on something more relevant for your first year. (4 speed servo shift was a waste of my life
)