Assuming we're talking about relatively run of the mill stuff, and not exotic beasts, the two best I know are...
Pegasus CT2K - about 120 kn at about 15 litres /hr
Grob G109b - about 110 kn at about the same consumption.
Both are plastic 2-seaters, although the latter is heavier and has at least some ability to carry a sensible amount of fuel and baggage as well as two adults.
G