FWIW..... I don't know anything about the photo processing, but just wanted to share my experiences with both stores.
Had BJ's memberships for about 15+ years (DBIL worked for them), but gave it up when he left them about 3 years ago. For the longest time our nearest BJ's was about an hour south.... then they opened another one about 35-40 minutes away. The place is always DEAD (not sure how it stays open). Great for shopping with no lines though. I LOVE that BJ's takes coupons and we always liked their tire prices.
That said, we got a Costco membership a few years ago and really love the place. Again, the nearest store to us is about an hour away, so we only go once or twice a month. But I like the foods and selections better than BJ's.... more fresh produce too. DH's get one of his long-term prescriptions there. And LOVE the samples they offer sometimes!

But they don't take coupons OR credit cards (so no air miles for those big purchases...

). And I'm not even sure if they sell tires! But the lowfat soft-serve at the snack counter is worth the membership price alone!
If I had to choose, it would be Costco over BJ's.
If I visited my local Costco more often I would definitely look into their photo processing................P