After years and years of riding and lots of different bikes and setups - my conclusions of the most long lived, grot resistant, smooth shifting cable options is as follows.....
Starting with the poorest.....
4, Gore type with multiple outer cable runs and protected inner cable- Just never got on with these at all. Seems like a great idea in principle but I found it not particularly smooth from the start and didn't last very long at all. Faffy, expensive and dont even bother trying to take them apart for cleaning without destroying them.
3, Traditional Triple run outers- cheap and simple, work great for a time but deteriorate quickly in wet conditions.
4, Full outers- Not as smooth as traditional but last much longer in wet conditions.
5, Cotic style split top tube + single run to the mech - Best of both worlds - just as effortlessly smooth as traditional. I dont know how long they last for as the set I put on 3 years ago still feels like new and I haven't touched them.
Of course buying quality XT or XTR cables is a must.