I'm in the market for a punching bag. I want to get a 6' Thai bag. My question is this... Does it matter what the bag is filled with? Which ones should I avoid and what should I look for. I see tons of bags on the net to purchase but it seems as though few advertise what the bag is filled with. I assume that water is bad for leaks and sand is bad because it settles? What else do they fill bags with?