leatherworking/skinning or engineering/miningFollow

First off you need to decide why you're doing it.

Is it to make money? If so forget engineering. In fact if earning money is your primary goal forget leatherworking too and just get gathering professions.

Is it for items that you can use? If that's the case I've a rogue can get decent use from crafted leather items espcecially at your lvl range with the nightscape and wicked gear. But the key is to keep your profession as high as possible so you're crafting gear that suits your level, rather than learning stuff that would have helped 5 levels ago.

But a rogue can also get a lot of fun stuff to use from engineering. Some of the best rogues I've faced in battlegrounds use engineering stuff. Engineering seems to be pretty pricey though, so it's typically not the best profession for your first char.