Personally I like to use this stuff:
http://www.meguiars.com.au/interior-...erconditioner/
I use it once every 3 months. Keeps leather looking tip top.
Apparently has aloe vera in it - does the same job to car leather as it does to our skin. Keeps it from cracking and moisturised - does a good job cleaning minor marks off as well.
Use it sparingly though. No need to slosh it on.