I use rubber.
At first, I thought that stamps would limit my artwork and that they would produce cards that look like every other so called "stamper". I am glad this is not true. While some stampers go berserk over some stamps (you will NEVER see me make a card using a "bella"...and if one ends up here, please call the police), I make a point to try to do something on every project to make myself unique. (Granted, I am a beginner; this is not always easy and frequently backfires.)
I have a favorite stamping company, for sure. It is called "justjohanna". The images are fresh and cute, and ideas flow easily for me when I review the catalogue. The ideas don't always meet the paper with the intentions my brain had, but I try! I like the "hand" of these stamps. That is the lines are not dark and heavy, the images are not cookie cutout computer generated looking images... they are fresh and fun. (I know I said 'fresh' twice, but it is true!)
It might be my interest in birds. I like to look at birds, I feed the birds in my backyard every day (sorry, Dad), there were numerous bird pets then and now. I can relate; I think of these little stamps like they are my pets. (I don't talk to them....yet.)
Some more of my favorites: