Per this page, there are nine Mbin instances with over ten monthly active users (MAU):
- fedia.io (458)
- tardigram.com (143)
- kbin.earth (131)
- kbin.melroy.org (38)
- thebrainbin.org (34)
- agora.energieincomune.com (30)
- rimworld.gallery (24)
- moist.catsweat.com (23)
- gehirneimer.de (13)
Fedia.io is the largest, though if choosing an Italian one is important to you, agora.energieincomune.com appears to be hosted there. The downside of using Mbin is that Interstellar is the only app to support it.