The not getting to fly part is not the frustrating part of the SO job. The frustrating part is that you may feel like an uninvited gueast at a party from time to time. If you have the choice between the 2, then I assume you are quite experienced. That can be a bit demoralizing as an SO from time to time because SOME senior officers in this airline will give you zero credit for anything. True story:
I was sitting in the jumpseat on taxi out and an alert(not using the words EICAS or ECAM to not indicate fleet) message popped up. The FO in the right seat grabbed his QRH and passed it in front of me to the relief FO sitting on the other jump seat.
I have had 2 or 3 incidents similiar to that one in the time I have been here. If you can let them roll off of you it is not a problem and you will be ok chugging through the SO phase as a means to an end. If these types of things are especially hurtful to you then you will be a very frustrated SO.
Other than that, the paid vacation, I mean the job, iis very good.
The housing can be very lucrative if you are responsible about it. Make sure you talk to various people when you get here about how to make the game work best!
Good luck