We use Ebb and Grow. See link at bottom.
Pros:
-Easily maintainable if you hook it up right the first time.
-Hydroton gives roots a lot of air(assuming you use hydroton).
-Works GREAT for veg, at least from our experiance it does.
-Expansion is realitivly cheap compared to the startup price(about $100 per 6 pots).
-Transplanting is easy(tho messy sometimes)
-Allows you to customize your setup. Buckets can be spaced accordingly to your situation. i.e. veg buckets right next to each other, flower buckets a few inches apart.
-The resivior can sit outside the room which is handy when you dont want to disturb your babies during their sleeping period.
-Roots can stay white for a very long time, yield can be incredible if you do it right.
Cons:
-Requires a LOT of space.
-If you expand, you will need a larger resivior than the 55 gallon.
-Cleanup is a B---- if you dont have the proper tools and materials. Cleanup between crops can take quite a long time, at least if you are thorough.
-Setup can be complicated and a lot of things can go wrong if you dont know what you are doing.
-Tubing can be stepped on and broken if not careful. Leaks can occur.
-You will need a high speed pump to empty and fill your resivior. Sometimes you will wonder off and forget you are filling it up! We have 3000GPH, 50GPM sump pump. Highly recommeded for any large size resivior situations.
http://www.discount-hydro.com/productdisp.php?pid=18&navid=4