For any colouring or just black I only use a shader, or for big areas I might use a colour packer which is set up somewhere between a shader and liner machine. But I wouldn't use a liner set up as it would possibly cause skin damage. I guess you are referring to machines and not needles? The only time I might use a liner and liner needle to infill colour is if it is very small letters or stars etc.
Personally for me its Got to be a packer m8, totally love them:icon_lol:
I would only use a liner for filling in if i was doing a tribal or writing and only for the pionts and corners of the tattoo to save time, also be carefull when using this method, its easy to make a mess of the skin.