What type of o-ring pick do you use?

Personally, I believe metal picks will get you in trouble. I've fixed a few guns that leaked with new orings due to damaged sealing surfaces. Hence my investment in the nylon picks. Plus, if you work on other things a lot, it's nice to have a pick that won't become magnetized. That's a lifesaver when using them to guide a tiny ball or spring without having it stick to the tool. 
 
I've been using a set of dental picks from Brownells for awhile. Works for me.

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https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/picks-hooks/stainless-steel-dental-explorers-prod9809.aspx
 
It is best to invest in a quality set of picks. I use a small jewelers screwdriver to remove most of mine. It is flat and less prone to scratch the sealing surface which is brass or aluminum in most guns. True Value has a nice set of American made picks that hold up well. Craftsman used to have a nice set too, not sure about now. Lyman used to make a nice set of plastic picks. I don't like the cheap Chinese picks because they bend to easy. I have resealed a bunch of airguns and really enjoy it, but good tools makes it so much more pleasurable.