finding a mutualite

It's helpful to have a local office where you can ask questions and submit your reimbursements in person, as well as having a drop-box for simple reimbursements where you don't need to check things beforehand. So check how far away the mutuelle offices are.

Do you have children? Some mutuelles offer more reimbursements than others for children's activities.

The refunds given by mutuelles are laid down by law so it's only the peripheral benefits which differ - one might offer a bigger 'goody bag' when you have a baby, mine gives pre-paid envelopes if you have to send them anything and pays in cash if you take your claim into the local office. In principle there is no significant difference between them.
If you are coming here to work, your employer might prefer to deal with one mutuelle but not all do.
Convenient location is useful but I know many people who do all their dealings by post and get refunds paid into their bank account so even that is not critical.

I have used euromut and had no issues.

I have used euromut and had no issues.

I have used euromut and had no issues.

Pop in to one in your neighborhood, and TALK to them. If they can explain what they offer in a language you can understand, then you'll be able to go in face-to-face and sort out any problem. If you can't communicate with the people in the office, it's not for you.

I have been happy with PartenaMut.

I would also agree with the suggestion that you visit the office near your work or home and see if they speak your language, since you may have a lot of questions in the beginning.