The Silicone cases do have more grip but one of my biggest reasons to go with Leather is the metal buttons. Whether its a garbage china-made $3 TPU case or a garbage China-made $40 Apple TPU case, having to press a button through a piece of rubber is annoying. Especially on the X which requires you to press that damn side button every time you want to turn on the phone.
I get leather every time and complain how slippery it feels. But metal buttons are important to me so I may have to stick a PopSocket on it. (I can't wait for the glares from people who see a $1300 phone in a $50 leather case with an ugly $3 toy glued on the back of it)