Do a search or two and you'll find several such threads. To summarize, both are used, both are important, and neither is objectively better except in relation to your tonal goal and personal preference. You'll also read that there are a variety of compromises with compressed wounds, oval outer wraps and stainless flats that have a roundish tone. If you're looking for a recommended string, you'll find a lot of those as well. If you describe what tone and feel you're hoping to achieve, you should get a good recommendation or two.
-bob
