The Fuji MF rangefinders are really something special. Out of all the film gear I've ever owned, including a Leica M6 with Zeiss glass, the GS645s is one of two cameras I've never been able to bring myself to sell. I've taken my best pictures with this camera. They're all great, so pick whichever film format you like best and just go for it.
Here are some pictures I've shot with it if you're interested:
https://www.flickr.com/search/?sort=date-taken-desc&safe_search=1&tags=gs645s&user_id=23530296%40N04&view_all=1 