Easier the better. Research suggests that the ideal pace for developing a range of aerobic adaptations is between 25-50% slower than 5k pace. For you that would be anywhere from 7:20 to 8:50 pace. Running faster than this has been proven to be less effective at producing training adaptations such as capilliarisation. I know this probably seems counter-intuitive as you can probably manage 6:55 pace, but that doesn't mean you should. An easy run should be just that.
A few different easy runs each week of varying lengths and at different paces (in that range) is probably ideal.
I myself ran all my mileage slower than 4:00/km (often as slow as 4:40) a couple years ago and ran 16:10 on a grass/trail course.