1. Animated - The sow was a great combination of fun and seriousness that worked well with the medium it was presented in. The toys were fantastic and really pushed engineering principles, and gave us toys that looked like the highly stylised characters on TV.
2. Robots in Disguise/Car Robots - Fun TV show with quite amzing toys (for the time, some of them are quite limited in today's standards). It also brought me back into TFs after giving them up during Beast Machines.
3. Prime - Haven't seen the show, but the toys give me that sense of enjoyment and engineering wonder that I found in Animated
4. Alternators/Binaltech - Toys were fantastic (for the time) and showed that a decent toy line could work without show support. The idea ultimately led to us getting the Classics/Universe/Generations toy lines.
5. Cybertron - Quite good toys, decent show. Wasn't outstanding, but had quite a lot of very good things about it.
6. Bay Movie - Mass market apeal with decent toys with real life vehicle modes was pretty awesome for a while. (Comes a very close runner-up to Cybertron)
7. Armada - First true entry into the TF multiverse - a new generation of Transformers for a new generation of fans. The minicons were an awesome idea. Some gimmicks were hampered by minicon ports, but the play pattern established was a fantastic idea.
8. Beast Machines - Not bad. Didn't really get caught by the toys. Watched the show in recent years. Not bad, but not fantastic, and takes itself way too seriously
9. Energon - Had some great toys and concepts. Also had some pretty aweful toys that were severly hampered by the combining gimmick. Show was pretty forgettable.
10. Machine Wars - Basically a line of repaints with no story support. Decent repaints though.