lol, it really relies on what you want to make. for some things a normal hard brush is handy, most of the times a normal soft brush is used. But there are also many brushes you can download, like smoke brushes andshizz
They are all good if you know how to use them correctly, also as others have stated it depends on what you are doing at the time. As there are many kinds of brushes each with their own purposes in PS