I find it interesting that many people have not done any research on this subject. If you are mining with air cooled system that I would agree that the S19 is a better choice, kinda. If in air you are better off with a T19 and then over clocking it since you would get between 95 and 115 TH out of it. It is more bang for your $.
But you are doing immersion. So I would suggest going with the S17s instead. You have to do certain things to prep a miner for immersion and there is a great deal of additional work to do this to an S19. The S17s take less work. The unreliability of the S17s come from bad soldering and some bad other parts. The heat sinks would fall off or there were problems with the connections causing the machines to
Overheat and breakdown. Running an s17 in immersion takes care of these production defects and overheating issues that plague these machines.
The cost per TH is one of the biggest driving factors for picking what to run. I would say the S17s in immersion will make you more money in the long run, you can also overclock them and get some fantastic hashrate from them.