Looove my rivers. I bag a beat in GL River for my flippy fairway spot. I can smooth the hell out of that thing and it will flip and ride dead straight for 300+ with very little effort and almost zero fade at the end all with <75% power. It is my woods/tunnel disc.
I also bag a heavy Opto (fisherman stamp) that is still nicely stable after 2 years and is quite domey. It will turn for me in the 75%-90% power range but will almost always come out of the turn to at least flat and has a nice forward pushing fade. I can put a little hyzer on it and it will flip flat nicely and ride straight for a long time while still finishing slightly left. I like it for when I want to turn it over and have it hold, or I have a tunnel shot I want to finish more left at the end. It is much more HSS and slightly more LSS than my GL making them a great combo.
I had a moonshine river that was quite a bit more stable than the opto, maybe closer to what everyone wanted a river to be (me included even though I love my GL for what it does). Unfortunately it completely disappeared on my last year. I need to pick up another one of those some time but I like very highly visible discs and moonshine doesn't stand out that great in the bushes.
Whenever I have "river troubles" I equate that to having "bad form troubles". Usually my form goes to crap the less amount of times I throw my rivers.