My take on Shanghai grocery markets:

1. Costco. This is the best option for high quality at a reasonable price. Yes the sizes are large but if you have a family and/or friends to share with, and a freezer to portion and store meat/fish, it can make sense. Many imported products including meat (good US and Aussie beef at fair prices), fresh and frozen seafood (with everything labeled as farmed or wild, not that easy to find in China), frozen dumplings, deli meats, butter/cheese, milk and yogurt, staples like bread/pasta/rice, snacks, beer and wine, etc. In my experience everything is sold at prices not that much more than the US. Costco famously makes most of their profit from selling memberships, not on the products. You need a car to go, but in my opinion it's worth it to do a haul every month or so. All of the products are high quality and relatively safe (I know anything can happen in China but I generally trust Costco's QC standards/process).

2. Hema (Fresh Hippo). If you live within the delivery area of a store, this is a great option. Delivery within 30-45 minutes and if I remember correctly the minimum order is only RMB 50 for no delivery charge. You can also pay for a yearly membership which gives you waived delivery fees and some discounts. This is the best option for vegetables/fruit (if you don't like going to the wet market), milk and yogurt (although more expensive than Costco), and anything else you need quickly delivered. In my experience the selection of imported or western products is not really that large, but you can find some stuff. Also their live seafood section is quite good, they have small Boston lobsters for RMB 99 each, not bad. They will kill and clean any seafood for you in store, you can choose this option when ordering.

3. Aldi. Great store, they are clean and well organized. Lots of interesting products and very reasonable prices. Just don't go here often but whenever I do I'm pleasantly surprised. Good bakery section (soft pretzels) and some nice imported (mostly European) products at good prices. Also I've had pretty good luck with their prepared foods (sandwiches and salads) ordered through eleme.

These would be my recommendations. I've been in the Gubei Carrefour and also the City Shop on Hongmei Road in the past few months and in my opinion both of them were seriously in decline. The Carrefour is strangely empty, both of people and with sparse product shelves, very sad because it used to be packed and thriving 10 years ago. City Shop also seems to have a basically localized product selection now. They used to be a great place to get hard-to-find cooking ingredients or items, but not anymore. Ole and City Super (and the similar stores that tend to be at B1/B2 levels of fancy malls), I find their products are good but way overpriced, rarely shop at these stores.