paper generally, though .pdf files are fine for reference at home, in game, paper - not had a problem with flat batteries on paper yet.
I did try digital list building with Flames of War, a few paid for lists, actually nice web site, easy to use, and produced useful references
then V4 came along and all the V3 stuff was taken down after a while, I've not bought anything in that format since
as others have noted, if its on paper it takes some effort to remove it from me, there are no "computer said no" moments and I don't find stealth updates are a problem
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