Assuming it's a 2003 Accord 4-cylinder automatic he's replacing, that was only EPA rated for 33 mpg, so if he's really getting 34, he's a hypermiler already and would do great in a hybrid.

I would suspect he's just saying "34-ish" because that's what his sticker said. You should make him actually measure a tank.

But if he's prone to quick changes in velocity, he's not going to do well with any hybrid. Maybe an Accord hybrid. Perhaps a Camry. But the HCH2 doesn't have power to waste on sudden accelerations/deceleration.

Would-be hypermiler