As a general principle .... everything else being equal .... fresh cold water prawns - and for that matter most seafood - will always taste better than prawns from warmer water areas. I guess it's because they grow slower and they work harder for their food. So you should be guided by the geography of the waters rather than anything else. The more Northerly the water sourcing ... the more flavour. Farming or non-farming effects taste less that the North / South consideration.

With larger prawns the majority will be farmed - and farmed in warmer water. So these prawns with almost no intrinsic flavour rely more on the flavours added when cooking - and their display value ie they are attractive on the plate - than their natural flavour. To be frank I think this is a food where eating with your eyes sometimes deceived the palate and it is curries, garlic, grilling etc that makes the flavour in wamer water prawns. To be fair, when you grill you intensify the latent flavour by water reduction and caramelising sugars therefore increasing the small amount of natural flavour. Basically I have yet to taste a tiger prawn or other large warm water prawn au naturel that has any worthy discernable flavour. It's what's added or done.

In the UK sadly our best seafood ie oysters, crab, langoustine etc is exported to other countries who appreciate it more - it is worthy of tears ..... but many UK people still think that the best local "prawns" are the very small fresh brown shrimps you can sometimes buy if you are in the right place at the right time.