Heart rate training- what to believe?

I'm currently training for 10 miles, hoping to up the distance after that. I want to improve my training results by trying out training based on heart rate, but there's apparently a lot of different (contradictory) information.

Some guides advise running most of the distance between 65-75% of the maximum heart rate, while other guides (like http://www.marathon-training-schedule.com/heart-rate-training.html ) call this the 'junk zone'.

What should I believe? It's hard to find out what to do.