I handle this pretty well in the toilet report below.
The Drake is the two piece version of the Ultramax, but without the slow closing seat.
It's more about looks than function.
Reasons for a one-piece,
Comes with the seat
No cleaning between tank and bowl
Tank doesn't need installing
Looks, purely subjective here
The Drake and the Ultramax, the first to come out with the larger flush valve and the long sweeping trapway have been doing very well.
Titan, a copy of the taller Drake that works pretty well.Dalton, a 2" flush valve siphon jet toilet, good bang for the buck, but hard for me to get at the moment. Discontinued in 2011
Quality does not look as nice as the Toto line though. Nobody buys the Titan if they look at the Drake side by side.