If you want a cruise experience, I think all of them will give you pretty similar ones. So pick whatever you want.
If it were me wanting to see southeast ak I'd book a ferry ticket and my own itinerary. You'd see more and smaller places and would be a degree removed from the bulk of other tourists.
Or if I had to choose a cruise company, maybe "uncruise." They at least try to be different than the big ships.
Also, Hardballer is right -- the earlier in the summer the better in terms of weather.
