I have cruise Celebrity Infinity 2006 from San Francisco to Alaska and I have cruised the Star Princess 2003 from San Pedro to Mexico. Alaska is a wonderful place, but I don't enjoy the Celebrity cruise. The food in the main dining room was terrible and not enough activites were planned on sea days. Also the public areas of the ship weren't kept clean. However, I did enjoy the entertainment (main shows) and the serve in the dining room was top notch (it really was a shame about the food).
Princess Cruise we did personal choice dining the food and service was very good. However, we took that cruise before Carnival took Princess over.
I haven't cruise Holland America. Celebrity normally has you cruise to the Hubbard Glaicer, which is a huge an amazing glaicer. I haven't cruised Glaicer Bay so I don't know how it compares. Here is some rough video of the Hubbard Glaicer from our cruise. YouTube - Hubbard Glacier Alaska