It depends on the environment. I believe indoors is more beneficial because you can control the environment but it's costly in equipment. Tho outdoors is cheaper in no lights or fans,timers,tents but more risky to bugs, bad weather and theives if on public land
Simple answer for a simple question, i would just say the effectiveness depends on your environment just as rarouni said. To give you an example of these such things ill explain a little. Outdoors has the benefits of a big yield but it is a one time a year yield, rather then indoor where its every 3 months. Lights, filters and fans are not used so you can turn that around and make better decisions for nutes, bug sprays, bigger pots etc. Indoors you have to buy these things no getting around it. Now that we have a few things said i want to go into the outdoor ideal environment ,5 acres of property, space between you and your neighbor because you cant have anyone see what your doing, i would personally want about 10ft by 10 ft square area to handle my growing/compost/anything related to weed. Also a small shed would be nice right next to it so i can smoke inside and hotbox and come out and watch the smoke leave ever so slowly while i am tending the garden.
Outdoor and match indoor quality if you know what youre doing, and you can yield tons more if you grow outdoors. http://farm7.static.flickr.com/6035/6343373632_6b88bc0631_b.jpg
I would say neither is better than the other. On the one hand you can get larger plants and crops outdoor Yearly, but on the other the indoor has a lot of benefits to like perpetual grow and you have complete control over everything. It all depends on your situation.
Outdoor growing resolves a lot of issues that closed indoor systems have but with certain trade offs. for example, growing outdoors frees you from dealing with lighting issues and the hit your wallet can take from buying to running the equipment; however, you loose the ability to force your crop into harvest. also, things like nut burning, ventilation and root bounding become a non-issue, but pests and sometimes unwanted pollination can occur. the pros of outdoor is that the plant becomes much bigger and the yields are closer to pounds per plant rather than ounces indoors. watering and feeding isnt as big an issue outdoors because once established, marijuana is pretty hands off. the biggest draw back is that your loose the control you would have otherwise growing indoors where you set the light schedule and thusly the harvest time. also, as mentioned, you can only get one, albeit BIG, harvest each year where as indoors its possible to setup perpetual systems. if you have the ability i would do both with your outdoor crop being your extra bonus.