tpau is very into negative G's -- the sort of thing where the coaster suddenly dips and goes into freefall, so you basically aren't attached to your seat for a bit, and are just being held in by the restraints. That turns out to set off my acrophobia very slightly -- not enough to wreck my enjoyment of the ride, but enough to temper it. This means that she really loves the Superman coaster at Six Flags, one of the most negative-G-centric coasters I know.
By contrast, I love positive-G spins -- the sort of thing where the G forces hold you steady in your seat as the ride loops, spins, and corkscrews. The sensation of sitting there as the world turns around me is just delightful. The result is that I prefer the Batman coaster, which is much more positive-G-centric, with lots of loops and screws.
Idle curiosity: what sorts of roller coaster do you prefer? Does the negative/positive dichotomy matter to you?