Drake is a 2 piece 1.6gpf toilet with a great flush
Eco-Drake is a 2 piece 1.28 gpf toilet with a great flush
Aquia is a 2 piece 1.6gpf /0.9gpf dual flush toilet (some people complain about the water in the bowl being to small and it leading to marks). I have not found that having one installed in our mens bathroom for the past 5 years, but i've heard complaints (which i believe you would find in any Dual flush toilet).
1 piece and 2 piece is exactly as it sounds, the benefit of a 1piece is that you have a cleaner looking toilet and no gap between the bowl and tank, but you pay for it.
For what you need and no problems i would go with the Drake 1.6gpf.