Hi,
It's all down to personal preference really. I prefer the codex colours but it's only because there are plenty of pictures available to try and replicate.
Advice (And you've probably already read some of this elsewhere) for painting the codex colours - I use:
Undercoat: Shadow Grey
Main coat: 50:50 shadow grey, space wolf grey (mix in an empty pot, add a small amount of water for consistency - this way all your models will be painted the same mixed colour)
Wash/Recesses: Devlan Mud
Highlight: Space wolf grey
Armour dents/scars - very little shadow grey, then underline the shadowgrey with a fine space wolf grey and for more depth, add a very small bit of skull white on the underline of space wolf grey.
Hope that helps! Great choice on an army to paint, the uniqueness of each model as a result of the kit makes each model fun to paint, I find boredom sinks in after the 5th generic space marine
For Russ and The Allfather!