Would you upgrade? Which brand is better?
Some teflon coated cables have a tendency to ‘gum up’ the housing and provide substantially worse shifting than non-coated cables.
Personally, I’d just use standard cables and housing and change them as needed. If you buy the stuff in bulk, you can recable a bike for about $5. It’d take a lot of cable changes to catch up with the cost of the more expensive cable systems.
If you’re experiencing cable contamination due to poor riding conditions, consider running full length housing. That’ll cut down down on the possible entry points for junk to get into the housing. That’s usually not an issue on a road bike, though it’s quite common on mountain/cross bikes.
I have not tried the Nokon cable set but have a Giant TCR Composite TT bike on order and when it gets here, it is getting Nokons due to the requirements of the internal cable routing. I will say that Nokon sure looks sweet on my friends Campy Record equiped bike but he went way overboard and bought both a silver and black set for brakes and shifters and then mixed the sets so that he has the links alternating black/silver!
As for the Aztec, they are less expensive than the Nokon’s and I opted to try out the shifter cables late last year. Let me start by saying that installation of cables is not normally a problem for me (it has been remarked that my garage workspace bears a strong resemblance to the Park Tools magazine ad - the one with all the tools haning on the wall) but the Aztec shifter cables ended up taking nearly 3-times as long as compared to Dura Ace cables! Word of warning, regardless of which cableset you opt for, if you do not get every last bit of slack out from between the segmented links, you may find as I did that on your first ride that after a couple of shifts under load, you suddenly have too much slack in the shifter cables and neither deraileur shifts worth a darn until you retension the offending cable - voice of experience. Now I have heard from some that while the brake cables are quite nice and very efficient - that is if you dont mind the fact that up front, the cable tends to droop when used with Shimano STI levers - it seemed to me that that the gear cables required constant adjustments of the tension using the inline barrel adjusters in order to maintain accurate shifting but that might have been the fault of the inline barrel adjusters. After using them about 4-weeks, I really was not overly impressed with the product as the links had discolored in some places and I opted to go back to DA cables when we upgraded to 10-speed DA.