Buy whichever one is cheaper; a used G90N for under 1800 RMB is a good deal, or you could buy a G90S for around 1500-1600 RMB.
The 171 is quite expensive, and it's true that it doesn't perform as well as a Q900 from the fourth generation, which costs around 1,000 yuan. However, the Fruit Core machine has more functions and also more bugs.