Both systems can lead to very wild games but also to more positionnal situations. 
The Owen (1...b6) has one advantage: it is not plaid so often and as a surprise weapon it can be very useful.
Now, when you look at the GM practice, you see that the Modern/Pirc is a lot more popular, which should mean that it is better. The Modern/Pirc contain a lot of gift in itself. It means that you have to know more about this opening than the Owen when you start playing it.
With the Modern/Pirc, you will win many games thanks all these tricks but you will also suffer many crushing defeats before you will be able to find your way through all the existing possibilities.
The Owen contains also some tricky lines (think of the f5 continuations) but, generally speaking, it is more "boring" - you will get quite often the very same type of position.
Short resumed:
- Owen: less work to start but also less variation in the game
- Modern/Pirc: a lot more to know but more variation in the game and at long term it might be more efficient as your "standard" weapon.