Hollow grind. I've got one of Darrel's hollow ground Apogees, and it handles slicing chores with laser beam-like efficiency. Seems to allow for a more precise edge when it comes time to resharpen- or maybe that's just my impression.
I too prefer a flat grind for most cutting chores. But a hollow grind does seem to take a slightly keener edge, so I can see it being better for cuts that don't penetrate up to spine depth. I also like convex grinds, but that's a whole 'nother story.
Most hollow grinds are sabre grinds. For a general-use folder, if it's between a sabre-grind hollow or sabre-grind flat, I'll almost always pick the hollow. But my fave overall is usually a full flat grind. If you're going to do a flat grind, do it all the way to the spine; if the grind only goes a little ways up the blade, you gotta go with hollow.
I used to insist that all my single edged knives knives have flat grinds and still try to when I know the knife is going to see heavy use. Then I ran into knives that were hollow ground with a big wheel (what Darrel said).
I am sold on them on some smaller fixed and large or small folder designs.
------------------ " Life is too short to carry an ugly knife."Steve F.