Lol, for me personally Debian is best OS even that JD is based on RHEL.
As you know you need 32bits OS to have working fort, otherwise when you go in fort you will be kicked to the login screen, but if you get 32bits you wont get more Ram than 4GB's, but Debian,RHEL,CentOS dont have this problem, because they have extansion that allows you have more RAM.
About Kimsufi they are good, but the problem is that their connection is only 250/500mbps and OVH and SYS offers 1GBps. Actually it doesnt matter what hosting company you will use. I personally know more than 3 ways for item dupe, and there are plenty of users that know it so I suggest you to work on security more than thinking what provider to choose.
Also play around with gdeliveryd configs, cause I can make players to DC with simple attack to the server just cause of bad configs.
Anyway when you're looking for hosting provider make sure he offers good connectivity also the server location is good so players have less ping.