I'd be a big fan of fractional metric.

Although if we really wanted to go crazy (this will never happen), we'd ditch base-10. It's a stupid base that we only use because of our fingers. Base 12 is superior and is actually the strongest defense of feet and inches (though yards can fuck right off). It has 6 divisors whereas 10 only has 4.

Base 60 is also cool (divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60), but that would also be significantly more difficult to teach children - it takes them long enough to learn the order of 26 letters.

And being a geographer, I adore 360 because it's fucking awesome to work with, and you don't get a better composite until 2520, which is just too much to deal with.