Ball Python questions??

[Snakefood]

1) Best bedding for a B/P???

say THAT 10 times fast!! LOL

I have:

white Aspen
Black Aspen
Carefresh
Repti-Bark

Which would you guys say the best substrate is from the above list. You can give other idea's, but take into account the above listed is what I have for the next 2 weeks until payday!! So pick one of those and THEN tell me me the better choice!!

2) Do B/P's burrow like corns?? do I measure the heat right on top of the UTH or on top of the substrate

I am sure there will be more questions as I go along. So keep tuned!!

Thanks everyone!!