G1:
Aside form what I listed above, I do also have a purely sentimental connection to G1 Swerve, as my mom used to decorate our birthday cakes when we were kids and she put Swerve on mine for my 5th birthday. And I did like the first Optimus and Megatron figures too, and Prowl was a favorite as a kid, but those guys were fragile for a little boy. Galvaton and PM Prime were much more sturdy upgrades.
Beast Wars:
We didn't really have G2 or Machine Wars around here, but Beast Wars showed up in force! I pretty much liked them all. I can't recall a single figure that I got that I didn't like. I even like TM Scavenger and Transquito. Some of my favorites though were TM2 Jawbreaker, TM Prowl, TM2 Dinobot, and TM2 Megatron.
Beast Machines:
This toyline wasn't a favorite of mine. In fact it really killed my interest in collecting TFs for a few years.
RID2001:
I saw Ultra magnus at Walmart one day and was hooked. I pretty much got all of this toyline that I could. Omega Prime is still one of my favorite TFs to this day. The Megatron is a wicked deign and looks great in bot mode. Rail racer is epic, Landfill was cool, Ruination and all the older toys were amazing to get! I loved the Laser cycles and the spy changers! I remember just getting my wisdom teeth removed during my college days for spring break, and my folks drove me two hours each way to the second nearest Toys R Us on the chance that they would have the exclusive toy. They did!
Armada:
I really harp on this toyline for the back sliding in articulation that we got for the past ten years at the point, but it did have some great toys. Demolisher and Cyclonus were two great toys that showed how the minicons could have been integrated better into the toys. Those two deluxes were my favorite figures of the line, other than you know, Unicron! That toy still stands up as a great Unicron toy!
Energon:
Well, the Terrorcons were an absolute blast! I loved Battle Ravage, Divebomb and Cruelock. I still have a giant horde of them in storage. Scorponok and Alpha Q were great toys to add to the collection too. The G1 inspired Megatron/Galvatron design was also a great little figure to have. The combiners were neat, but not up to par.
Cybertron:
This line gave us the best Optimus Prime since G2 LROP! It was an epic toy that still looks great to this day on my Prime shelf. I also love the Cybertron defense toys.
Classics:
Early Chug wise, its hard to say which was my favorite, but if I had to narrow it down, I would say that the Seeker mold was my favorite of this toyline.
Animated:
This entire line is gold. No complaints, no favorites. They re all awesome and I have just about all of them. I don't think I could choose one over the other.
TF Prime:
I really like the basic Vehicon mold in this series. It does a great job at being a menacing looking toy as well as being a troop builder. THe secodn version of Optimus is epic as in Wheeljack.
WFC/FOC:
Bruticus. Such a great combiner.
Generations:
Metroplex. That was a great update to the classic and started us off with some epic Titans.