unless you think you are going to fly SQ soon do it NOW. SQ is truly amazing, it will make your AC pod seem like a 3rd world seat, on a dusty old plane.
you need to understand there is NO COMPARISON, between AC and SQ.
So with that info decide whats important to you
You will always get to fly in an old J seat on AC thats narrow with ancient IFE. You might not have the option of trying something amazing.
So unless the other people have flown both airlines recently they don't understand the difference.
Who cares about customs in SFO you wont wipe the smile off your face from the SQ seat.