For wildlife- Kenai Fjords out of Seward. Intense glacier viewing- PWS out of Whittier. If you have the time both are very worthwhile. I always and have gone many time on Kenai fjords boat tours, less often for me with the glacier viewing. I like Phillips out of Whitier , Kenai Fjords tours and Major Marine out of Seward but Renown also gets good reviews. You need a sailing of at least 6 hours on the water. Take precautions if prone to seasickness.
I agree with Karen on the Kenai fjords tours. I went on a 6 hour at the end of my last cruise and just finished booking the Full-Day cruise with Major Marine to kick-off my next cruise in September. Resurrection Bay is full of marine wildlife and birds...my only regret last time was that I went for the shorter tour. Oh, and don't let a cloudy day make you tempted to cancel. Dark animals like the Orca whales and sea otters are much easier to spot in "white sky/white water" conditions. College fjord is wonderful as well, but more for majestic glacier scenery. Check your cruise itinerary. Many of the cruises do spend some time in College Fjord. If they don't and you have the opportunity, do the Fjord for the scenery. Happy sailing!