If you go for less than 6 hours on a boat tour from Seward, you don't leave the bay. That means your chances of seeing whales greatly diminishes. You definitely can see whales in the bay, but I have seen them much more often on the 6 hour or longer tours.
I find the time on the 6 or even 9 hour boat tours goes so fast. But then I am excited about all that you see on those tours. That is one reason why Major Marine with their buffet doesn't excite me. I bring snacks with me and eat when I want, not when they tell me to. I am outside on deck looking for whales and other wildlife for much of the trip. But as was said, everyone is different.
I was just coming in here to ask about these tours. You seem to know your stuff, so maybe you could give me some advice. I will be in AK in August and want to take a boat cruise and see the fjords and some wildlife. The Major Marine 4 hours evening cruise fits best into my schedule, but I really want to Kenai Fjords tours 6 hour national park cruise. I would have to shift some things around to do it, but I'm thinking it's worth it. I'm an avid photographer with a big giant zoom lens or two that will be joining me. Am I right in my idea that the 6 hour tour will show me a lot more of the iconic fjords? There is a huge price difference and the schedule thing, so I just want to be sure I'm not going out of my way to get a similar experience.