There is no good or bad. The best is the one that suit for you. CentOS and Ubuntu represent the two main factions of Linux. The CentOS faction is headed by RedHat, the package managers are RPM and yum, the package dependencies are bad, yum is slow, SystemV style. The Ubuntu faction is headed by Debian, the package managers are dpkg and apt, package dependencies are the best, apt is convenient, BSD style. If you are a beginner, it is recommended to learn CentOS. There is a certain foundation in learning the Debian faction. Ubuntu can be thought of as an unstable version of Debian. Suitable for daily office work.
Regardless of the kernel version , the kernels used by all Linux distributions are the same, the only difference is the installed packages.
CentOS is the community version of RedHat. It is compatible with RedHat's RPM installation package. It is generally used as a server. The pre-installed content is also the content of the server. Except that there is no RedHat service (we won't buy it if you want money anyway), it is not much different from RedHat. Package management is generally managed with rpm or yum.
Ubuntu is based on the Debian 
distribution and the GNOME desktop environment. It also has a KDE version. It is a more popular distribution. It has enhanced graphics functions. There are desktop versions for general users and server versions. Because its desktop version is more beautiful, there are more multimedia software and the support of ubuntu software center, it is also easy to use for ordinary users, so it is more popular. Its server version also has nothing to say, it's not too much. Package management generally uses apt-get .
To say which is better, this is mostly a subjective feeling. If you use it as a server, of course choose CentOS, or Ubuntu Server version, if you use it as a desktop system, then use ubuntu desktop.
I have been using ubuntu desktop for many years, but I feel that linux is still far behind windows in terms of multimedia and software support, and basically cannot be used for entertainment. There is no way to install dual systems, because the family wants to play QQ games or something, it is really inconvenient under linux.