It’s a matter of preference. I can only offer my opinion:
1- Ubuntu is super easy to use and configure. It’s also very well supported. I use this for all of my servers, and I host a lot of sites, some of which are very high-traffic, well-known ones. Be sure to secure your server (Google “hardening Ubuntu primer” or something similar). Choose an LTS version if you can (Long Term Support).
2- CentOS is usually used for servers that ISPs use to host websites. Just throwing that out there. I find CentOS more difficult to use, but if you’re looking to put cPanel on your server, then choose this one. Same disclaimer goes with the server hardening.
Now, this is just opinion, and the preferences I currently have because of my experiences. I’ve been doing server work for 17+ years. Your mileage may vary. You can always install both ($5 a month per server) and see which one you like better. But those are the two main ones I would recommend. Actually, ignore my preference for Ubuntu and try both. That’s the best path.