I have a 2003 Allegro Bus and have not had any of the problems that I read about on the Tiffin forums. The slides have worked perfectly and I have no soft floor issues on the slides either. I checked the flooring in my wet bay area and it also is very solid, so no issues there.
The only issues that I have had to deal with were engine related(leaking fuel pumps), and a new refer cooling unit. The coach itself has been trouble-free.
As with any coach, check it closely for water leaks and good service records.