I actually use both depending on what my goals are at the moment. When im bulking up ill use animal pak, when im performing more athletically i will use opti-men.
I have found that animal pak gave me better lifts but poorer endurance when it came to sports abilities and that using opti-men didnt pump me up in the gym but made me less prone to fatigue and dehydration when performing in rigorous activities outdoors.
If your mountain biking in the rockies take opti-men, if your slamming weights at golds gym take animal pak.
These are my opinions and are in no way scientifically based. Thats just how each affected me and my performance.