I prefer to stalk on my good two feet but when cover runs out I go to a belly crawl. The key to not making noise is moving real sloooowwww.
A friend of mine, an ex special forces member, says that if you have to crawl to your odjective to avoid beening seen or heard make sure you have time. He said that if you are moving more than a foot or two in one move you are going to fast, 1" to 6" in one move is even better. His way of thinking is that if you had to go 20-30 yards on your belly it should take you up to 30-40 minutes, longer if in dry brittle/crunchy conditions. His way does work I've spent an afternoon on a hill waiting for him to see how close he could get to a muledeer. I didn't see him until the deer busted out of his bed and my freind stood up out of the grass within 2 feet of the bed. He has a lot more patience than I have.