I've not seen a Kopp guide for 70-80 yet...
Kopp's guide has easily been the fastest for 1-70 out of the guides I have tried.

My second choice is extreme leveling, which isn't as detailed in what to do, but does have a good order to follow.
Kopp will say, talk to npc-name and take quest-name. Or take all the quests from the guy on the left.
The Extreme Leveling guide will say take these four quests, but not tell you which guys have which quests.
If you're leveling your second set or fifth set of toons, it won't matter so much but Kopp's guide is better for your first set of toons.

Penn's World has the best tradeskill guides I've seen so far.
In the leveling section for a guide it shows routes to take for the herb, mineral etc.
So if you open the zone map in one window and their route in another, you know where to go for the quickest farming of the herbs used to skill up.
The guide doesn't show you routes for all herbs, but it does for all herbs it suggests to pick in a given leveling up range.
One guide with all future upgrades, which included inscription even though BC was new when I bought the Penn guide; cannot complain about that.

As with all guides, they're charging for information they have compiled.
If you were patient enough, you could gather the information free for yourself.
You don't need to try six paths to decide which is most efficient with a guide, but you pay the author a bit for their time.
In the end, you don't need any guide to progress, the a good guide lets you progress quicker then doing the research yourself and then using it.
Unless of course you were also in the beta and did your research before the expansion release date.