The way I have heard it is to get your base in before you work on really high intensity. I sort of think though that different methods work for different people. Remember any exercise you can do regularly is better than the ideal exercise that you never or seldom do. Quantity and consistency will trump nonexistant quality every time.

Me, I like mileage and some intensity. It works for me. But if you find it daunting to do mileage and love to do hard intervals, do them as long as you don't beat yourself up.