I grow both. Indoor because you have better ability to manipulate and control conditions. Outdoors because, regardless of potential for natures many adverse conditions, you just can't grow serious monster plants indoors like you can outdoors. Here is a pic to make my point. This pic is about a week old, and plant is growing 2-3 inches a day with close to three months left in the season.
outside, I let nature do its thing with a bit of organic help. I grow nice mild smoke I don't care about brand names, my shit is my own breed oldschool taste and a nice zippy high