I just returned last night from my 5th trip to the Kenai Peninsula. I would choose it over Denali (and I love Denali!)
I haven't done bear viewing flights because of the cost. However, I've seen bears in the Russian River / Cooper Landing area which you'll be driving through on your way from Seward to Homer. (If you see a bunch of cars pulled over to the side of the highway and people taking pictures, it's a good bet someone has spotted wildlife.)
I would take the 9 hour Kenai Fjords trip. It is absolutely spectacular!