I used to prefer the leather. I had the midnight blue leather case with my 6 Plus. I gave it up pretty fast, not because of its quality, but because I guess I picked the wrong color. It looked so sad. So I gave it to the person who bought my 6 Plus.
With the 6S Plus, I've made a radical switch to silicon
and am very happy about it. I love the texture and the perfect finishing, the inside lining that keeps your iPhone snug and comfy.
And the colors are much nicer, too.
Being a silicon case, it does gather some lint - but far, far less than usual silicon cases do. I always carry around those little wipes for glasses, so when I clean my glasses, I give my iPhone & case a wipe, too. So no lint really worth mentioning.