I have laptop with 4GB RAM. Would it be better to get Ubuntu and then install Xfce on it, or to get Xubuntu?
Ubuntu uses animal names for release names not by accident. If you want a fossa install fossa. If you want to play Pokémon and evolve your own customized animals, Ubuntu is open source so you customize and configure it any way you want to. If you've decided to install Xfce, Xubuntu is offered as a convenience because everything you need to run the Xfce desktop environment works in Xubuntu out of the box, and it's better to run a cleaner operating system (native default Xfce in Xubuntu vs. installed Xfce in Ubuntu).