I googled your question and found the following explanation. It seems the 18/10 may be a little shinier than the 18/8 but from the below and other sites, I gather there isn't much difference in the two.
"When buying stainless flatware, you will often see the terms 18/10 stainless and 18/8 stainless. Many people do not understand these terms so I will try to explain them to help you select flatware for your table!
18/8 and 18/10 Refer to the Percentages of chromium and nickel in the stainless stell alloy in flatware. The 18 refers to the chromium content. The 8 or 10 refers to the nickel content. Chromium content gives flatware its strength and the nickel gives flatware shine and rust resistance.
Basically there is very little (almost NO) difference between 18/8 and 18/10 stainless. They are used as marketing terms for flatware companies like Oneida, Gorham and Yamazaki. Usually manufacturers make flatware from stainless steel grade 304 which is 18-20% nickel content. Stell manufacturers make stainless grade 304 with 8.2% nickel so flatware companies can call it 18/10 stainless."
These numbers don't refer to the weight of the stainless flatware. Most of the time, flatware companies will make heavy weight flatware, but the steel itself doesn't make them heavier, it's the style and design and way it is made, not the steel.
The best way to buy stainless flatware is to find a style you like and try it in your hand to see how it feels. Good premium flatware brands won't bend when you use them as intended.