Really depends what you want the suit for. If its a one off thing such as a wedding then the high street stores will do you just fine. They can be quite cheap and they do allow you to mix and match the jacket and trousers, which is great for the odd-shaped fellas amongst us.

If its for everyday work use then my advice is to splash out on something a bit more expensive. They will wear alot better, last you way longer and won't look like you dragged it through a ditch after every wear. Try Remus/Magee or Baumler in this category - cant go wrong with them.

Your man on the top floor in Best on O'Connell Street really knows what he is talking about, unlike most of the unhelpful bluffers in other places. diffneys are also good and you can't beat the personal touch provided by the smaller places.