Really depends on the skill level. An Avistar can be a great 2nd.
muddpup had a great suggestion with the Super Sportster, or Fourstar 40, 60, or 120.
A little hotter plane? A Something Extra, however, IMO, you really do need to have a programable radio to tame the Fourstar and the Something Extra. Those controlls are huge compared to trainers and need dual rates.
Have fun!