The larger market/supermarket like shops like Big C, Tesco Lotus and bulk shops like Makro are going to be your best bet.
Then smaller chain supermarket like Big One are often in the smaller shopping malls in the center of numerous towns and existed before the larger Tesco/Tesco Express became popular. They are still going mainly because they are still important landmarks in a downtown area.
Then you have shops that cater to foreign/'refined' tastes. Tops Supermarket, Villa Supermarket, Gourmet Market and the like found in or near major shopping areas like Central World, Siam Paragon, EM district, and only in major cities that are likely to have enough Tourists, Expats, or HiSo traffic.
7-Eleven, Family Mart, et. al. are like convenience stores open 24/7. Tesco Express and Mini Big-C are usually 7-11-'like' in their setup (open 24/7), but can still have the same prices/sales as their larger counterparts, so they can often be cheaper than 7-Eleven. Since they tend to be close-by each other, you can check both and see which ones give you better deal. You know a town has 'arrived' when a 7-Eleven or Tesco Express has moved in.
Other lesser known chains were mentioned in the OP: Fresh Mart (CP Fresh Mart), Begato, Foodland, etc. Some of these are more like specialists shops that only sell Begato meats, for example.
Also, it is nearly always to your advantage to sign up for their membership cards. You gain points and rebates that can be used for even more discounts. Places like Gourmet Market, you need to request the tourist discount card before you checkout: 5% off your total. They used to hand them out like candy but I think now you must give them your name and signature (you'll see the list); but that might only be for foreigners not sure. 5% is better than 0%. Places like Tesco or Big C it works out if you will be staying for several weeks or visit Thailand regularly; otherwise, just borrow a friend's card.
