I did an absorbancy test on the things I own, just to see how everything compares. I figured I'd post my results. For each thing, I tested 2 items and averaged the numbers (they were all very close). To test, I slowly poured water onto the item until it started dripping. I then hung it on a spaghetti drying rack, over bowl, until the dripping stopped. I poured the water from the bowl back into the measuring cup.
Here are my results and subjective thoughts:
Diapers:
Infant CPF: 12 oz
Regular CPF: 14 oz
Premium CPF: 19 oz
Sugarpeas Size 1 Organic Cotton diaper only: 6.5 oz
SP Snap in doubler: 3 oz
SP Doubler: 5 oz
Pampers Size 3: 32 oz
Inserts:
med. night LJ for BB: 10 oz
sm. JB: 4.5 oz
med. JB: 5 oz
Luke's Drawers Doubler: 6.5 oz
Blue MF towel from Target: 8.5 oz
White MF towel from Target: 8 oz
Subjectively, the prefolds soaked up the water the fastest. The hemp did the best job of spreading it around. The MF towels were both the slowest to soak and slowest to spread. The Pampers was actually the hardest to test, because it was slow to absorb the water, but kept on absorbing if I left it sit for a couple of minutes.
I don't know why the color of the mf towel made a difference, but my white towels are much more staticy too.
ETA: the LJ was a nighttime version. I only tested 1 Pampers so that I didn't have to throw 2 away.