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i'm in Orlando and go to AK a fair amount. Like others have pointed out, there' really isn't a good side. If you can, though, sit in the back. This way you can swing your camera around and not get in anyone's way.
i usually shoot with the 70-200, but I think you'll be ok with the 400. However, there will be times when the animals are just too close. If i had to pick between the 2, i'd take the 70-200, but I know you'll wish for the 400 sometimes.
That doesn't give you much of an answer, but animals are unpredictable and there's no way to tell. the 200 will give you more flexibility throughout the day though.
Keep in mind: the ride is very bumpy, it can be frustrating shooting on it. Also, light might not be ideal earlier in the morning unless there are extra magic hours. But, the animals may be more visible/active.
Finally, here's one of my Lion Shots from AK