Torstein Johansen has a nice post on useful Emacs packages. As it happens, I use all of those packages except auto-complete so I’m certainly in agreement with his list. The post includes animated gifs so you can see the packages in action.
His list is mostly concerned with ways to speed up【Meta+x】 and with word completion. If you aren’t using these packages, you aren’t getting the most performance out of Emacs. But what about auto-complete? I haven’t run across it before but I’m going to give it a try. Why not? The rest of those packages are very useful and I wouldn’t want to live without them.