We were on Coral Princess in May. We had the all day cruise in Glacier Bay. It was absolutely breathtaking! We saw a glacier calf, which was a wonderous experience. We had a balcony and enjoyed all the scenery from our balcony.
We didn't go to Tracy Arm, so I can't give you any information about that. There have been several posts here about Tracy Arm and it sounds awesome, too.
I don't think you can go wrong either way. Guess I didn't help much, but I wanted you to know that you won't be disappointed in Glacier Bay, if that is the option you choose.