Kevlar for pull pull.
I got mine from my local hobby shop. Just one word of caution with kevlar. Make sure it does not rub anywhere. It will fray and break. I could have lost a 25% Extra due to this. Luckily, I had a reason to pull off the covering and saw it was already fraying.
I'd suggest getting the steel cable set up. It's just as easy to install and safer IMO.