In theory, the shorter the cable, the better. This matters much more for guitar, as extra cable length will begin to roll off the high end of the signal. With a good cable, you won't begin to notice this until the cable is more than 15-20' (and that's with guitar).
+1 on that... there is so much hype and spin out there about cables, it makes me crazy.
I buy good quality cables in the $18-$25 range. Planet Waves, DiMarzio, Fender, Neutrik, there are other
good brands, but I've had excellent service from these.
So I don't fall for the cheapest prices, and I don't fall for the hype that promotes the $50 instrument cable.
Middle ground works fine. Well known brands are better than no-name junk. Always carry spares, so that if
one fails, you have another handy. Avoid coil cables, they look cool and retro but break down too easily.
That was true back in the day when they were all that was available, and it's true now.
In my experience, cables fail because of damage caused by stepping on them on a crowded stage or practice
area. Tuck your cables into your guitar strap to keep from stomping them yourself, and don't allow MCs and
jack booted lead singers to stomp on your cables onstage.