They both have their pros and cons.
Indoor
Pros - Ability to control every aspect of enviroment, can force flowering at an early stage of growth, can reveg plants, easier to check progress rather than hike 2 hrs to your plants, and probably more I'm forgetting. Not to mention the obvious security from annoying neighbors and low life thieves.
Indoor
Cons - Initial setup cost for a good indoor grow can be quite expensive, plan on spending +$300. Space limited=Yield limited, unless you have a room with 16 ft ceilings (which a friend of mine does have
)
Outdoor
Pros - As long a you find a very secluded area which recieves good daylight, you can grow some huge plants (7 ft+) that can potentially yield several pounds
per plant. That is a HUGE pro. Setup cost is cheap compared to a sophisticated indoor grow.
Outdoor
Cons - Biggest con in my mind would have to be the low life thieves out there who will rip off your hard work without thinking twice about it. Wildlife will possibly eat/trample your plants (chicken wire fence prevents this), pests are harder to control, you have to make regular trips to check the progress and feed the plants, and you have to let mother nature take her course, meaning you have zero control over the enviroment. It can also be quite difficult to find a good secluded spot to grow in that gets good light and has easy access to water.
For speed of harvests, you can't beat a hydro indoor grow. For high yields ie. indoor plant vs. outdoor plant, the outdoor plant will usually take the cake. If you live in a city you probably want to spend the money to get a good indoor grow going, however if you live out in the country you might consider finding a good spot for an outdoor grow.
There are many things to consider when deciding between and outdoor grow and indoor grow, and it really depends on each grower's personal situation.
Now the real question, which is better? Neither. They're both different, and both have their ups and downs.