Can i get advice on the difference between these and which i should go for.
i want to also install on a server and administer through ssh setting up different apps.
thankx in advance.
All of your prospects Slackware, Debian and Gentoo are capable and good at running as a server. Since you were from ubuntu you will feel very much at home with its mother Debian. Gentoo and Slackware will pose you newer challenges.
I use only Slackware and BSD but Gentoo is a very respectable distro as far as I can observe in their documentations and user fora. Decision is up to you.
May it help.