I have personally used a number of different bags, Iron Duck, StatPack, Thomas Pack and some other brands. For me I use Thomas EMS Emergency Medical Pack. This is what is stock on all ten of my trucks. They are large enough to hold all of the first line equipment, medications and supplies. And most importantly they don't weigh a hundred pounds!!! They are compact and you don't spend all day searching for that one thing you needed and halfway through you forget what you were searching for.
On the volunteer service that I am on they use the Irons Ducks and we have three bags to take in on a serious call. The airway bag, general bag and drug bag (not a small one but a full size bag). Its a workout for sure!!!
I think the biggest issue people have is they they put too much in there first in bags (one service had three complete IV sets and two of all airway supplies).