Anything in particular? I love Sapphire Princess. I've been on Sapphire Princess and Island Princess numerous times. I like Island Princess for Alaska for the reasons I mentioned, and also for the Panama Canal--especially since Sapphire Princess is too wide to travel the Canel :-). But I have been to Hawaii on Island Princess too.
The ships have slightly different deckplans but the venues are very similar. The cabins on Island Princess are just slightly smaller but the open deck areas seem more spacious and uncluttered. The food and service and very comparable. I think Sapphire Princess makes better use of its aft deck space. Both are beautiful and well maintained. I'm sure you would enjoy either one.