Ihave both and they both have pros and cons & I get different stuff at both. But if I had to pick one, I think BJ’s is better.
For instance, Costco only has their own diapers & Huggies. Bj’s had their own brand, Huggies, Pampers, and Luvs. Similar situations exist in every product category.
Costco often has packages so big, they only seem reasonable for the largest of families and/or those with tons of extra storage space. My boys like cottage cheese and Costco sells a huge tub that is practically a bucket while BJ’s has a tub that is a little bigger than the SuperMarket.
Bj’s has a deli, seems to carry more organic food on a regular basis, has better (longer) hours, and accepts coupons. I like Costco and they definitely have good items throughout the store but Bj’s is a little better to me.