Having sufficient factors. The only change I would do (if I could) is to make the metric system use Base-12. That would be something truly better because one-third would now be 4; quarter would be 3; half would 6; three-fourths would be 9. Compare that to 3.3333; 2.5; 5 and 7.5 of something.

Just like who hexadecimal is very natural in 8/16/32/64 bit computing, the "real life" usage of measures would be much easier if it was in Base-12.