The most powerful is the ofna truggy box but it is bigger than I like to carry in my pit bag. The best starter box imo is the mugen starter box, not as much power as the truggy box but considering it is smaller and designed very well it gets my vote as the best one out.
If you want more power go away from the 12v battery. Run a 14.8 lipo that helps out a ton! And it makes your starter box wayyyyyy lighter. Trust me put a 14.8 lipo in it and you will be very happy.