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Staedtler Lumocolors. You can pick them at at Staples or probably any office supply store. Them always stick, so no card prep is needed (even on Bowman Chrome). It is what Topps uses for players to sign with.
I was lucky to find lumocolors last month at a closeout at a local office depot that closed it doors.
The situation will dictate which pen I use. If I am not around that many people, I use the lumocolor. When the crowds are crazy, I use a sharpie. I also see how a player holds a pen.