You want the wings to flex!
I've been on some flexi winged 747's!
I've never been on a 747...thanks for the warning.
I don't like wings to flex the way the Airbus wings flex/shudder/shimmy.
Maybe my distrust of some planes has something to do with this accident which happened a mile from my house when I was a young teenager.
We thought the Russians had blown up/bombed Argonne National Labs. Many of the volunteer fireman in my town later died, fairly young, of heart attacks.
I've liked flying enough to have worked for UAL (reservations) for a year.