If it's hot, we park it under a tree. If you go late, just pick anything, since BB gets crowded. However, the best tip is to pick a chair near a landmark, so you remember where it is after going on a few slides and the river ride!
When I went with then DS9 by myself last July, we got a chair near the Ski Patrol so that I could see DS while he played but be able to sit at the same time. We got there about 20 minutes before opening and it worked out fine for us.
Go RIGHT from the entrance bridge and keep going... you'll have to go over another bridge, etc. KEEP GOING toward the back of the park. Up overlooking the lazy river and near the exit of the family raft ride. There are decks and sandy spots out of the way, with quick access to the lazy river and a few water slides.