Best: Series 2 - The final was so close between Shayne Ward and Andy Abrahams, both were great. There were lots of good acts - Brenda, Maria, Chenai(?), Journey South, Conways were good singers but boring, a decent boyband...and of course Chico.
Also...series 5 - Cowell decided to revamp the show and make it bigger and better, after the full series 4. Quite a few good acts, JLS, Alex, Ruth were great. Did get a bit sick of the fawning over Cheryl Cole.
I loved series 7 too, but all the manipulation ruined it - Waissel, Cher, 1D favouritism. Cheryl Cole/Cowell love-in.
Worst: - last series for me. Thought it was terrible, although Little Mix were a good group.
Series 4 was terrible, looking back, but at the time I enjoyed the Sharon Osbourne dramas etc.