"BEST" and "TRAINER" are pretty wide descriptions, personaly the BEST trainer for me was the SPAD Debonair, it was cheap, tough, easy to build and had lots of on line back up, it's also available as an ARF if you dont want to build.

have a look at www.spadtothebone.com
having said that the SPAD BUHOR probably builds quicker and has a better wing loading for slower flight.

Or ifyou dont mind the extra bit of work the SPADet is a nice looking plane