[I found a very bizarre but informative article][1] about 8 reasons why one should not use ENUM.

Even without the article, I know

- [there is no easy method for adding new values][2], some techniques are very high risk
- numbers should never be used
- only use strings (@DTest already mentioned this in his answer)


  [1]: http://komlenic.com/244/8-reasons-why-mysqls-enum-data-type-is-evil/
  [2]: https://dba.stackexchange.com/questions/6547/can-i-rename-the-values-in-a-mysql-enum-column-in-one-query/6548#6548