The later in the day (especially the last two departure times are much less crowded, but the also won't let you sit in the first few rows due to weight distribution. Also sit toward the center aisle if you don't want to get wet. :)
Half way in to the ride, they stop at McCovey Cove by AT&T Park for a "photo op" & I recommend that you wait until then to use your camera. The twists & turns during the ride are very unpredictable (part of the fun) so the risk of losing the camera is quite high.