I second what John_VV said.
Don't be fooled that Kate and Gedit look very bland when you first start them up. In Gedit, going to "View-->Highlight Mode" opens all sorts of markup options. Invoking the "Tools" menu on Kate does the same.
In both of them, you can edit appearance and, to an extent, behavior, but the options are located in different places on the menus.
vi (actually, most distros ship
vim or "vi improved") is a horse of several different colors; it is extremely powerful, but provides no menu--you must learn the commands or have a good cheat sheet; a web search will turn up several available on-line. I like using it, but I must say I'm barely adequate at simple editing in
vi. The command set is very terse--the creator of vi was quoted in a recent issue of
Linux Voice as explaining that, when he was working on it, he was using a 300 baud dial-up modem.
Kate is my own favorite, but either Kate or Gedit works quite nicely when you learn your way around them.