Hi Antoine,
First, I apologize for the response in English. I am hoping that your English is orders of magnitude better than my French.
Although this question gets asked a lot, there is no definitive answer. It all depends on the type of analysis and the number of users.
The best places to look for answers are:
The Galaxy Deployments Catalog
This describes how Galaxy is deployed at different institutions.
(And if you deploy Galaxy locally, I strongly encourage you to describe your instance here)
The GalaxyAdmins Survey
This is now two years old, but it contains a lot of great information.
Espérons que cette aide,
Dave C