I am intrigued by the responses here. And folks certainly have different goals for liners.
My goal is probably somewhat unique as a reseller. One, I display tools for sale in tool boxes and Lista type cabinets. So I need liners that look good and don't allow the tools to move or have the liners move. Second, since I sell boxes, I need liners that look good and look like liners. Third, I need them to be reasonable in price. I usually buy 10 rolls at a time and do so multiple times a year. That is why I use the yoga mat from 5 Below as they are $5 a roll. And the liners don't shift and the tools don't move. I can't say that about most of the liners that come in tool boxes.
The one exception is the liners that come in Mac boxes. It is the sticky type, probably similar to someone who posted a link to ebay. I think the Mac liner is a bit thicker though and is head and shoulders the best I have seen. The problem I have with the ebay link liner is the price. At $27 bucks a roll. At 10 rolls, that is $270 vs $50. Doing one box for yourself, no big deal, but I go through 30 rolls a year and that adds up quick. And while the sticky liner is best, the yoga mat ain't that far behind.
To the guys who use cardboard, you have a great point about absorbing moisture and oil and no liner will do that as well, except maybe the pig mat. And the cost is certainly low

But I would think tools would slide on cardboard and that would drive me nuts.
To the guys who use carpet, do the tools stay put, and I mean real put, or do they move a bit?
So what are the goals you have for liners?