I read Joe Lewis (the famous Karate man / Kickboxer ) saying that working with a bag more than 150 pounds is not nessesary, even for power developement. I'm not a boxer (I'm a fan And an athlete, Track, basketball). I know that my hardest punches on ANY bag are when the bag ****ing fly's afterwards, and I have to wait for it to come back when I hit it again which is frustrating. MIND you, if I was to miss an opponent in a street fight one day, I would expand a lot of energy missing with that kind of punch. Maybe there is some science to smaller bags then, like conserving energy as you throw snappy punches. What's best, I'd really appreciatte an answer to this question.
100 pounds bag, or 200 plus pound bag that you can punch in to oblivion becuase it's not moving too far away (or hitting back ofcourse..)

the bigger the bag the stronger it makes you i would say go with whatever you want. i have more than one and all but one is over 100 lbs. and i am about to get a 200 lbs.

If you are moving a 100 pound bag too much, you are probably pushing, rather than punching, it....

150 pound bag is fine because if it starts moving on you it goes slow relatively. like throw a left hook and when its going right throw a right hook so you hit it while it has momentum behind it

then hit straight like never let it get to far away and you'll be fine