Im setting up a server , should i prefer OpenSuse leap or RockyLinux and why?

Does it even matter as one is based on SLE and other on RHEL and both are fairly stable distros. Not sure if there is any difference between them.

Lots of differences But underneath they are the same Linux but some things may have different versions, somethings may or may not be installed as default. It is mostly a matter of taste.

USA vs. Europe, Germany.
Leap with KDE, support for ppc64le, s390x and others.
Leap has 1.5-year support period and requires update every year.
Rocky Linux is too new and IDK how long it will be supported.
They claim:

Current planned end-of-life: 31st May 2029

RockyLinux is the replacement for CentOS - I think it will get good support.