Best adjustable "ultra-micropipettor"?

[the End]

Has anyone had a chance to compare the various adjustable volume 
ultra-micro pipettors on the market? I am used to using 5 fixed 
volume Oxfords for 1-5ul samples.

In air-displacment designs, I see Gilson P10, Finnipipette,
Eppendof, Oxford "Benchmate", Calibra(Wheaton), and a few others.
Anyone spot any signififcant differences? Do any of these 
aliquot 1 ul of enzyme stock reasonably similarly to a fixed volume 
with a plastic capillary (ie. Oxford)?

(Special tips a definite drawback)

Thanks much,

Jim
J. Graham