I've used all three as well. One thing I found was if I edit files in QuickOffice or OfficeSuite, they will no longer open in DocsToGo. Plus, DocsToGo won't let you change input method. I often change keyboards depending on what I'm typing and which part of the app I'm using (spreadsheet vs document). That made DocsToGo cumbersome.
The issues I had with QuickOffice were with formatting. An office doc had the last paragraph with no new paragraph market (pressing the enter button to go to the next paragraph). QuickOffice didn't show the entire paragraph. I opened the file in OfficeSuite, pressed enter and saved, then it looked fine in QuickOffice. The next paragraph didn't keep any of the previous formatting, though.
OfficeSuite has become my favorite right now. Formatting does what I expect, and it works pretty good. I would say they all have their own quirks. It's more about finding which one works best for you.