Putting cost aside, I'd chose to buy Lidl fish over Tescos. We don't buy meat. Tinned goods I buy are baked beans (which DH reckons are better than any other brand), chickpeas, kidney beans, sweetcorn, tinned mackeral - all equally as good as other brands.
Other products I buy and am more than happy with are bakery, bread, pitta bread, tortillas, hummus, coleslaw, cheese (good and lower price), yogurts, eggs, some frozen (pizza, fish, odd ready meal, veggie), museli, rice, pasta (I think it takes a bit longer to cook but we do have wholemeal), fruit tea, decaf coffee (DH had no idea decaf until he asked to swap and I told him), crackers, crisps.