In reality, it's your call. Maffetone is a conservative aerobic training zone, ideally don't go over the max of 180-age, and work up to 10 beats below it. I was happy working at 27-137bpm, and increased my running pace from 11:30 min miles to 9:00 min miles over 2.5 months. Not fast, but working at a low HR and being able to train for longer with no ill effects.
I would go with Maffetone, it is conservative, but you will get the aerobic adaptations, like increased mitochondria numbers and improved efficiency. It might be a slower method of getting fit, but you avoid adrenal stress and increased cortisol production (none of these a problem for our sprints and lifting, you just don't want it during prolonged aerobic activity)