Both has its upsides and downsides.
Outside Pros:
Huge plants, The sunlight is the best source of light
Outside Cons:
Stealth is harder, gotta watch out for rippers and helicoptors, only one harvest per year (unless growing low ryder)
Indoor pros:
Total control over environment, perpetual harvest (year round), grow is right there not a hike away.
Indoor cons:
It's in the house so forced to "own up" if caught. Smell can be an issue. more $$ to set an indoor op up.
So in a nut shell both are proven methods but its up to you to decide which on is for you. Myself...I prefer indoor easier to maintain. but love the giant outdoor plants that yeild huge.