Never done hydro, but I hear good things if you know what you are doing. I like Indoor soil because you are basically mother nature. You can grow much faster indoors because you decide the variables. There are no clouds, hurricane winds, or harsh rain. Also if the power goes out, your babies should be O.K., but I know in hydro if the power is out too long then you are in deep doo doo.
Some good things about outdoors are
1. No electric bill
2. Don't have to check on them as much.
3. Not a lot of worrying about police (If Guerilla Growing)