Colouring edges?

I'm returning to paper modelling.
In the past i have never coloured the edges of my cuts. I want to start doing this to improve the look of my finshed models.
What should i use?
Sharpies (i have young childern so have a range of colours)
Colouring Pencils (i have a cheap set of water colour pencils)
Wax pastels (I have these in a limited pallet, basicly primary colours)
Which would you recommend?
Thanks
RH