I've only done mini golf once at WDW and that was at Winter-Summerland. It's really cute & a lot of fun for a little while. Definately not a 'must do' for us but it was something to experience once. Never been to the Fantasia one though.
Here is a link with information/pics from the Winter Summerland mini golf:
Winter Summerland MiniGolf
This is a link to the Fantasia one, doesn't look as exciting to me though.
Fantasia Gardens Miniature Golf