Is this only G1? Devastator is my favorite but I have a feeling Liokaiser is going to take that spot once I get him!
That I own: ROTF/Universe Superion, mainly because he's the only one I own Out of ANY combiner: RID Rail Racer, the first all-train combiner. I like trains, and he's one of the few combiners who have big brains in addition to brawn (in comparison to like, Leokaiser?)
Road Ceaser. The US release ones are great, and the first four Scramble City ones hold a special place in my heart, but Road Ceaser is just amazing, and has much more fun individual figures.
For awesomeness I'd vote Predaking, but Piranacon is my favorite. It's the only '88+ G1 bot I own as a matter of fact. Just got done stripping all the worn stickers on him and applying the reprolabels. Took me like 6+ hours! I did'nt get all the stickers on Snaptrap removed because they were in such good shape.
Out of the ones on the list its clearly Predaking but he's not favorite combiner of all time. Omega Prime or Sonic Convoy in their on screen incarnation an execution as a toy.
Tough choice, I always thought Devastator, Bruticus, Menasor, Computron, Superion, and Defensor were really cool. I ended up choosing Menasor though, no particular reason... just had to choose one.
Predaking. Just because the amount of intimidation he brings is unmatched. Being G1 (American) toon based gets bonus points from me. Honourable mentions go to: Devastator - the original old school badass, with six bots! Bruticus - The eps with Starscream as well as variety of vehicles make him very memorable (got the Encore on pre-order. Can't wait!) Superion - the Autobot's first combiner and a great mix of personalities within the group Menasor - cars, only they're Decepticons! Cool!