My two cents are: if the release is 1,000cfs or less then I vote for the lower; if its somehow 1,500cfs or more then the upper. In between 1,000-1,500 I don't know. I've just done the lower the last couple of times I've been on the Millers and wouldn't mind changing it up. I thought the upper was a lot of fun the first time I ran it when it was around 1,500cfs...only so-so the other time I ran it around 1,000.
I'll have a good time on either section so in the end, I don't really care too much.
I already know Paul's vote. Anyone else want to chime in?