I'm wondering if I should use grease or oil to lube the larger seatpost that drops through the frame on the Dahon eezz d3. I'm using silicone oil on all the moving parts of the fold but I'm not sure what to use on the drop down seatpost.

On a vertical surface like a seatpost or seatmast, I like grease. Oil can get messy and leak into areas you don't want it to, whereas grease tends to stay put.

Xootr folding bikes recommends applying Boeshield T-9, wipe excess off, and let it dry overnight. Not saying that applies to your Dahon though. Seems to work without being a greasy mess.

Boeshield is what I use too. It's wax based rather than oil based and leaves less of a sticky residue to collect dirt.