Customisability is the main draw. Maybe additional features like: support of high colour modes; browser-like tabs; transparency; background images; tile-ability and other interface integration things; ability to show images on the command line; etc.
But as many people have said here, whatever comes with your distro is almost certain to be fine for everyday use, and probably has more customisation than the average user will need.
Edit: Saving on making a second comment; GNOME Terminal is my distro's default and what I use. I also have the venerable xterm
installed just in case something goes wrong with GNOME Terminal and I absolutely have to have a terminal right that second. Haven't needed it yet.