Unfortunately, the best aurora are during the dead of winter when it's -40F. The summer is when everyone comes to Alaska, because that's when you can be outside without dying, but it's daylight 24hrs so you'll never see it then. I wouldn't recommend coming in the winter, unless you REALLY want to see them, because there's not much else worth doing that time of year.
I once dreamed I built a heated, enclosed tent/shelter with an acrylic dome for a roof and was sitting in it in the middle of the Alaskan wilderness, watching the aurora while comfy warm.