At one time and age, I would have said wheels. These days, at my age, I am 100% with noglider - handlebar choice, hands down (pardon that not intended near pun). My Motobecane Gran Jubilee has gone from drop bars, to mustache bars, to upside down mustache bars, to flat bars and finally, the bell ringing north road, or something very similar.

Yup, for me, it is handlebar choice, coupled with an appropriate steering stem reach...