If it's proper SQ (and not Silkair.. which you don't get any benefits on as *G unless it's SQ *G) for 220 USD vs. 90 USD for Jetstar, for RT, I'd DEFINITELY go with SQ. Especially if you don't have free lounge access with Priority pass.. (the PP lounge is slightly above the level of the lounge SQ puts *G into.. so if you've an unlimited *G pass, I'd probably hit there..)
Assuming lounge access isn't free (but discounted.. like 27 USD per person) for you, 4x lounge access would already be exactly as much as you'd pay for the SQ flight.
Also, if you're both *G and flying SQ, you could probably make two other flyers very happy by guesting them into the lounge
Also, if you book SQ, you don't have to worry about luggage fees/gate checks or whatever.
Seriously, with the difference just being 130 USD, and you being *G, you really should got with SQ in my opinion. IF lounge access is free for you via PP, and you REALLY want to go with the cheaper option, then maybe Jet Star could be an option. But even then.. I'd probably prefer SQ. It's just like those LCC could cancel any flight late, have delays, whatever. With SQ, you've at least a reasonable carrier behind you.. (please note, if it's Silkair and not SQ actually flying, all would turn around again.. suddenly properly putting Jet Star on top again)