I did the half-day cruise with Marine Tours. They are good, ship is clean and all you have to do is pray for good weather. Our cruise lasted about 5-hrs and when there isn't much to look at, 5-hr feel a bit long.
We saw a small whale breaching on a beautiful sunny day. However, we didn't see any Orcas/Killer whales on this half-day tour. From a couple of people we spoke to, people who did the full-day cruise with Marine Tours did saw Orcas.
Just keep in mind Seward rains often. Our first day there, we did sea kayaking in light rain and I thought it would stink, but our guides were good and it turned out to be a wonderful experience.
As for Exit Glacier, we had a rental car, so we just drove up. It's located not far outside (8 miles or so) of Seward. It's not as grand in size as I thought but it was still pretty amazing to see a glacier up close.