Personally I find "best" very subjective, as noted from the previous posters. As far as versatile, that would tend to be a numbers game. There are many numbers thrown around as to the numbers of transferable M11, M10, and M11/NINE machineguns in the registry. It is my understanding that there are around 3,000 M11, 8,000 M10 and over 17,000 M11/NINE models that are transferable. Development of accessories is expensive. With fewer possible customers, developers would tend to develop products for the biggest market. So developers tend to make products for the M11/NINE as it is a much bigger market. For sheer numbers of accessories, the M11/NINE would have the greatest number.
For me price and availability tends to be most important. A local deal, especially when that might be at lower than market value has more appeal than a specific model multiple states away, at or above market value has the least appeal. As time goes on and transferable prices continue to rise, the think that the thicker sheetmetal stronger construction of the M10 will tend to lend itself to more possible conversions requiring the the additional strength of the M10 receiver then the thinner lighter construction of other models. But that is certainly down the road.
Scott
