I'm not an OPA, but have done the Officer jobs in the Command Post and on the OP (CPO and FOO).
OPA is better every time.
I remember the Command Post job as being 5 minutes of your hair on fire (moving, setting up position), followed by long periods sat in the back of a truck on the radio (still high pressure and concentration - not monging it).
The OP job though is nearly always on the move - if you stay still, you'd better be in excellent cover. Moving from position to position, moving to get eyes on the target, dismounting to get closer etc. Plus on the OPs you will be further forward, so if you want action, go OPs - they are the guys doing the FST (Fire Support Team) jobs on operations - air, aviation, guns, MLRS, Mortars the works.
That is just my opinion, admittedly biaised because of my preference. Hopefully some CP dudes can give you their side.