No two choices should have the same ID

In any case avoid create different fields with the same Guid OR - and this is important - the same internal name.

This is never checked by the solution packaging mechanism or while adding or installing the solution to the solution store. The errormessage "No two choices should have the same ID" occurs, if you for e.g. try to add an existing field to a sharepoint list.

Be sure to check this from time to time during development-process and before setup your solution to the production server. If the system is up and running, it's very difficult to do changes here...