Seasons 2 and 3 of TF:A were tops for me on TF shows. Easily because the toys are so wicked and the G1-esque characters and designs. But, also because the storyline was pretty good. I guess I can't imagine what they'll do to top that, except continue (maybe with Galvatron as leader).
But a transition from ROTF to Transformers & G.I. Joe in 2011 could be a possibility.