Before starting I must mention the website Distrowatch here you can get information about all the linux distributions.
Now starting over it depends on what kind of things you wanna do with your system.
If you wanna explore the system like hacking or something : Kali
If you want everything installed system and don’t want install basic software : Mint
Web server : Fedora ,Ubuntu if you don’t have experience can go for Redhat.
Cloud: I don’t know much about this but after reading about Solaris, Redhat and Ubuntu Cloud. Redhat seems better than others. CentOS is also a great option.
Lightweight: Debian, You can use XCFE desktop with any linux.
Windows like system : Zorin
Security and penetration Testing: Backtrack, Kali. Since backtrack stoped giving updates go for the second option.
At last you want overall package go for Ubuntu. Though it seems very heavy for simple machines due to unity desktop. I think for this much is enough.
Want any other suggestion? Do comment.