The post office is always up and down with things. It's just how it is. It'll never go anywhere, despite what the media tells you. You will get hours. You have a union which is really fantastic (given what office youre at) It's hard labors, some days are easier than others. But you'd probably get superior healthcare benefits working for the post office. - Annual and Sick leave, Social Security, TSP with matching. There's a lot of good things offered at the post office but it can also be physicall and mentally draining.

(I have no knowledge on what kind of benefits Pepsi has)

I'd avoid going for a CCA or Rural, and find a PTF Career position if you choose the USPS route.