RIDE seems to be a popular choice by many here and I know the developer of RIDE frequents this forum so help is not far away.
There are many things that influence which is the best, including personal preference, and organisational requirements. I suggest you check out the Robot Framework Page, select the “Tools” menu and then click the “Editors” tab, there is a good list of whats available there.
My personal preference is to use the Atom text editor with the Robot Framework plugins, as this works best for me as I was using Atom before I knew about Robot Framework, so its a tool I was already familiar with.
My personal advice is to try a couple then decide what works best for you, or enables you to develop test cases the quickest.
Hope this helps,