Lets say you have a high scoring game like geometry wars, why type would you use for the score and how should you handle overflow?
Depending on the scoring system in your game and the type you use you may never need to wrap. For example, an unsigned 64-bit integer can hold a maximum value of 9,223,372,036,854,775,807. Long before games get close to that most would start displaying problems rendering a number that long in the UI. It would also take an awfully long time to rack up a score that big so it's not really worth worrying about.
Depending on how you implement a leaderboard (i.e. use a third-party system for online scoreboards) then the format of the score may already be decided for you on their servers.