this article which brought to my attention that not all are quality. Sometimes they are just coated with stainless steel, and then there is the nickel quantity in it - nickel stops it corroding so the more nickel the better.
Did you know stainless steel should not be magnetic? If it is, then it isn't quality stainless steel and will corrode, bend in the oven etc.
To sum up, the best stainless steel food grade that you can get is 18/8 or 18/10 standard. (The 8 and the 10 indicate the nickel level and that's the highest available apparently).