This is a very good question and something I've been considering alot lately as I'm about to start my 2nd grow, 1st was in soil and took 11 weeks it produced a good yield but, I'm wondering if I could do better,
As I'm only considering starting my 2nd grow I'm definately not an expert, from looking through alot of info from the web, books and speaking to people last weekend at
http://www.grow2010.com/ , all the points raised by Sunny D are spot on, I've also heard hyrdo can be more expensive, One of my concerns is that hydro is suppossed to be less forgiving, Which as a new grower is definately a concern,
I've been looking into this again today and have come across DWC Deep Water Culture, Which is a type of hydro, I think most hydro systems work from drippers from the top to bottom of the plant, but DWC works from bubbling water from the bottom to the top, It's suppossed to be easier than normal hydro, produce a greater yield than soil, and seems to cover the benefits of both types of mediums,
As I've mentioned I'm new to growing so hope some one can shed some light on this to help my knowledge grow !