I do not use Vim-Jedi but from what the doc says, the plugin allows completion using CtrlSpace.
Supertab is another plugin which remaps Tab to a sensible autocomplete behavior.
The author only suggests to use supertab if you want to use the Tab key to trigger Vim-Jedi completion (This is easier than remapping the key by
yourself in your .vimrc
).
This means that you can use Vim-Jedi without supertab if you like its original completion with CtrlSpace. IMO you should just give Vim-Jedi a try without supertab and when you're comfortable with it, you'll see if you want to use supertab and make your choice.
Jedi
(for python) and replaces theSuperTab
functionality.