Lets just say there are a few you may want to try, BUT...
the "best" is most suited to a specific mission, what you need to carry and above all, personal preference.
I have used Blackhawk brand, both the STOMP 2 and the Tactical Special Operations Medical Pack (a new one with the molle on the outside). Good things about these are that they are readily avail, and you can easily find accessories for the outsides to carry more gear. I find you can easily overload the STOMP 2. It would be more suited for in the back of an amb or for an advance care provider/PA/MO bag. The Stomp has 2 compartments for gear which may be a problem if you have complicated patients which need things from both sides. The Spec Ops bag works for me as a coy medic. I find it holds almost enough stuff. When its full, its full, and there isn't allot of other stuff I NEED to put into it.
Another good bag is the Tactical Medical Solutions R-AID bags. They are comparable in price to the Blackhawk Spec Ops bag, but much smaller.
London Bridge also makes bags, but I have yet to see any of them.
If you want to go old school, our old style med bag holds just the right amount of gear for a platoon and coy medic, esp in the dismounted role. Unfortunately without a good deal of modification of the strapping and adding of attachment points for patrol pack accessory pouches, it just isn't real good by itself. But its compact size is good when strapped to the ruck.
