I'd say a few things determine what makes money and what doesn't.

Demand - When I started doing Skinning/LW, I bought all my leather off of the AH all the way up to Knothide. Stacks and stacks of leather. No matter what kind of leather you put up, I'm fairly certain someone will buy it.

Knowing the Market - learn which items sell quick that LW's make and concentrate on flooding the market with the appropriate leather. See if the other mats are in abundance on the AH, then undercut the lowest auction by a good amount and you'll make quick cash. Works the other way too... If theres a shortage of a certain type of leather that you have a lot of, up your price and  gouge your customers. =) If they think they need it that bad, they'll pay for it. When the market gets an influx of that mat, lower the price.

Id say this could be true with every mat available on the market. Being shrewd will fill your coffers.