I'd do a flip-flop hub with a freewheel on each side. Something like 65GI for the flats, and 45GI for the hills. You can accomplish that with a 39t chainring, and 16t and 22t freewheels. With such a large difference in tooth count between the two freewheels, you'll probably need to lengthen your chain when you get to the flatter part of the ride.
People with different levels of fitness will likely have different opinions regarding gear choices, and they'll all be right.