There is a large gulf between Fedora and CentOS. With Fedora/RHEL/CentOS you have a choice:
Bleeding edge. Less well tested. (e.g. in F8, gdm defaulting to not allowing more that 16 users and then ignoring its config file, for several months before a fix was in place.) Have to upgrade every 7-13 months.
By the time you get the software it's already old. Then you get to live with it for, nominally, 18-24 months. Longer in actuality.
It is (unofficially) possible to "side-grade" between them. But to go from Fedora to RHEL/CentOS you can only do it by hanging back (as much as you can without sliding out of the security update window) on your Fedora upgrades until a window opens in which the new RHEL/CentOS packages are newer than your current Fedora packages and you can do it.
Ubuntu gives you a different choice:
Reasonably well tested release. Current, but not bleeding edge. At any time, you can choose to upgrade or not. If you upgrade to a non-LTS release, you can upgrade or skip the next 2 releases (12 months), but must upgrade by at least the 3rd. (18 months).
If you choose only LTS releases, you can go 3 years between upgrades for desktops, and 5 years for servers. You can, of course, upgrade to a non LTS release at any time.