How does OPM, NPM & GPM percentages figure in fundamental analysis of the stock - I don't recall anything mentioned about these things in Graham's "Intelligent Investor". Some of the stock I like seem to have a fall in OPM, NPM, GPM (as percentage) in 2007 as compared to 2006? What does this signify?

Which of these is better metric for valuation?
1.Operating Profit Margin (OPM)
2.Gross Profit Margin (GPM)
3.Net Profit Margin (NPM)
Please guide.

Net profit margin. because this is what is left with after adjusting all the administrative, selling and other expenditure.