I have used newspaper, reptibark, cypress, aspen, and brown packing paper. I have one bp in a tank and one in a RBI cage which as far as humidity is concerned, is like a tall CB-30 tub.

These are my thoughts on each:

Newspaper: cheap, easy to clean but imo not so good in the tank as it doesn't add to the humidity. Also, you can't spot clean and will have to change substrate every week.(one of my snakes is a biter, so this was a problem.

Reptibark:Looks nice, doesn't usually stick to food items, adds to humidity. I really liked it for my tank but got too humid in rbi cage. Doesn't clump to poop that well and would recommend putting one sheet of newspaper underneath in case snake like to burrow.

Cypress: Kind of messy for my liking, shoots up humidity if you don't bake it first. try to find 3x milled cypress if you can. I only could find 2x milled which had some big pieces in it.

Aspen:This is really good if humidity is not really a problem. I have heard that this stuff can mold if you spray it too often. Worked great in RBI cage(I will be switching back to it). In tank not so good on its own but when mixed with repti-bark, it work out well.

Brown packing paper: I got a 30"x20' roll at staples for about $4. I think it looks better than newspaper and is a little more absorbant. Overall it has the same problems as newspaper though.

Recommendations:
If you rather spot clean every week go with aspen, repti-bark, or a mixture of the two. Just remember to put something underneath it.

If you are a neat freak and feel the need to do a full tank cleaning every weak go with newspaper or the brown packing paper.