Split outers, maybe the inner matters more. Need an inner that will cope with the weather on the exposed parts. Good outer (e.g. SP41), ferrules and boots are key to avoid crud getting in and fraying ends.
Whole run inners, just get SP41 outer and any old stainless steel inner will do. Found zero difference between posh brand inner and cheap stuff, so long as the outer is lubed inside (which SP41 is).
Buy the outer off a reel for the length you want (or plenty more than you need so you have a read supply for the future). Way better value than pre-cut length packs.
Look after the ferrules though and get the cable length and angle to shifter right. Odd angles bend at the shifter and the ferrule splits, then the crud gets in and the outer frays and rusts up.