vi has been standard editor for years, and lately vim has replaced vi in most systems. Many users won't even notice many differences between vi and vim. However, vim is much more powerful and extensible than plain vi.
Anyway, editors are one of most religious decisions in linux world, so I won't start with typical blablabla....
crontab, as many other commands like vipw or vigr use $EDITOR environment var to launch the editor. just change it to nano, emacs or whatever console editor you prefer.