Stiffer but the flex of your boot really depends on how you ski and your weight and height. Trust me skiing on a boot that is to stiff sucks don’t go down that road
A boot that is too stiff is a problem. A boot that is too soft is a problem. Find the right flex based on your strength, weight, height, etc. and you will have a boot that flexes how you need it to.
I have some full tilt boots with a 6 flex (no idea what the conversion is) and my other boots are a 130 flex race boot and I can butter so much better in my race boots that it’s not funny. My race boots have more heel hold but the flex also plays a role too. Also it’s easier to soften up boots then it is to stiffen them and stiffer boots usually have better materials (like better plastics in the shell or a denser liner or whatever) so I’d go with the stiffer ones.
“The boot also boasts a soft flex, ideal for nose butters, tail presses and any number of creative moves in the park and across the entire mountain. “ full tilts which are soft flex