As Scoot and Jetstar Asia compete PER-SIN but the 3K flight leaves PER at 2am and the Scoot flight leaves around 5pm I am guessing that the best price garantee won't work in this case due to the time difference in flight times?
Jetstar uses A320s for PER - SIN, so no option for upgrades there. The few times I've checked, Tiger has better pricing than Scoot or Jetstar, so I'd price beat Tiger instead.