boot stiffness

there is no "best" or "should be," only preference.  typically, people who like more response and power will go with a more supportive boot, while people who want more mobility, forgiveness, and the ability to tweak easier, will go with a less supportive boot.  you will tend to see most people who ride natural terrain, who like going fast, and are powerful riders, wearing stiffer boots.. and you will tend to see people who spend a lot of time in parks and on rails, tweaking, spinning, moving around, wearing less stiff boots.  that said, there are certainly plenty of jibbers who wear supportive boots, and plenty of the opposite who ride softer boots.  preference is king.

It's all preference. I prefer super stiff boots as it's what I'm used to, but it doesn't mean all I do all day is carve groomers. Being marketed as a "freeride boot" or "jib/streetstyle" boot is an oversimplification of boot selection. Some jibbers might just like very stiff boots and will just lace them more loosely for more range of motion. Or you do can what you want with what you have. The dealbreaker for boots should always be fit and comfort.