help w/punching bag info appreciated

I want to purchase some punching/kicking bags but I need some education.

1) leather or vinyl
2) heavy bag -vs- thai bag -vs- not so heavy bag
3) Which type of bag develops what?

If anyone knows of good articles, please help.

...Thank you very much

 1) leather lasts longer

2) an 80-100lb bag is standard. thai bag is great for low kicks but not really that special. go to thailand and you'll see them kicking regular heavy bags more often than not.

3) heavy bags are about developing power but it's really on how you use them.  ex. you can use speed, movement etc but in the end it's a static target, won't help your defense.