This idea is similar to the badges for the public groups badge, but very minor.
The idea is to have "badges" made for one of each of the types there are, like a Fire-type badge, and so on. And the user will be able to select, perhaps a maximum of, three badges. One being their most favorite type, the second being their second favorite, and the third being their third favorite. And to avoid clutter, only their first favorite type badge would display in their posts, where the Donor image would usually stand, while the other two would be displayed somewhere in their profile.
If not, then the favorite type could just be displayed in a user's About Me section, with or without the badge.
EDIT: Whoops! Forgot to do this! It seems like the plan would be to go with the latter idea, where a user's favorite type would instead be placed in their About Me section.