Personally, I prefer the metric system because it is based on multiples of ten. This make mental math much simpler when using the metric system rather than the US system. Scientists sometimes have to make calculations on the fly, or many calculations in a row. If these calculations can be done accurately with mental math, you can save time.
For example, it is much easier to convert grams to kilograms using mental math, since one gram is one thousandth of a kilogram. It is much more difficult to convert ounces to pounds, since one pound is one sixteenth of a pound. I would need a calculator if I were converting between pounds and ounces frequently.
Another reason I prefer the metric system is because familiarity with the metric system allows me to read and understand scientific results produced overseas. Can you imagine how complicated it would become if every country had its own unit of mass? Standardization makes international collaboration much easier.