We tend to use Carrefour for the normal weekly shop as we find it's the most pleasant to shop in - wide ailses, well it, reasonable well organised and not too crowded if you go at the right time. The one downside is their bread is rubbish (surprising for a French company!).
Then we go to Mega-mart for the bits and bobs Carrefour doesn't stock, and when we fancy a few luxuries!

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