I think most people seem to think hydro is better simply because nearly all the hydro that is grown is really high quality. In other words, if someone is going to take the time and energy to grow hyroponically they probably aren't going to grow schwag. They're going to grow on a small scale, use high thc strains, and baby those girls until they are just right for the pickin. A lot of the natural grown is large scale, has a lot of seeds, and is grown for quantity, not quality. If the same amount of tlc goes into growing natural, however, you'll get the same high quality as you would with hydro.

One thing about hydro is the plants are busier and yeilds are higher due to the controlled nutrients. Here's a link to an article with good info:

http://www.overgrow.com/article/22