(Basically, kg is the perfect unit of mass and if you disagree you are a heathen and should be burned)
Of course this is an imperfect world. In a perfect world I'd like a meter chosen so that gravity is, to a good approximation, 1 m/s at sea level, and I'd like all of the units to be in base 12. (Easy divisibility by 3 is often very useful.) Including time, so that one doesn't have the awkward 3.6 factor converting from m/s to km/h. And our number system should also be base 12, and...I think you can see that I'm willing to complain about lots of things which will never change.
To be earnest, octal is quite a nice base. Or -2 (minus two!). Or 10, but with digits from -5 to +5, though that representation should be redundant, I guess.
To speak of redundant representations: Fibonacci numbering is also interesting (http://en.wikipedia.org/wiki/Fibonacci_coding). Or skew binary numbers.