Star Wars: R2-D2 (This was before I saw the movie in '78, when the figures first showed up in the store. My older brother who had already seen it got Luke.)
GI Joe: Destro (I loved his chrome head, and he was a bad guy for my Star Wars figures to fight. Later I would buy lots of Joes (especially Cobras) to fill out my Star Wars adventures as the 80's wore on. Eventually my friends and I wound up cracking them all open and mixing/matching parts to make our own superhero characters out of them. For all the Joes I owned, I never played GI Joe.)
MOTU: Trap-Jaw (I had avoided this line the first times I saw it in the store, but once I saw the commercial for Trap-Jaw I really wanted to play with him. From there I started watching the cartoon, and for 1983-84 this was my go-to toyline, snuggled right between the death of Star Wars and the beginning of Transformers. He-Man and I were never "exclusive," but we had a great affair. I even invented a subline called "Cat Island" that was a story about where Cringer/Battle Cat and Panthor came from, and included a whole bunch of other cats like Cringer's love interest, his best friend etc etc. I drew pictures, and wrote stories about Cringer's return to the island to stop evil Panthor, and how hard it was for him because without He-Man he couldn't turn into Battle Cat and instead had to handle it as himself. My first fanfic!)
Transformers: Windcharger & Hound (I saw the Decepticon cassettes in the stores first, and was really intrigued by them but didn't have enough money. My younger brother got Windcharger and he was the first one I got to transform. Once I had watched the cartoon miniseries, I really wanted to play with them. My mom worked at a department store and happened to be taking care of the toy section the day the big Autobot cars first showed up, and she called me from work and asked me which one I wanted--my immediate reply was Hound because of the impression he had left on me from the miniseries. This became the toyline that took me to my teenage years when I started to transition from "playing" to "collecting." I remember getting Powermaster Optimus Prime and realizing I was too old to play with him, but I still appreciated it as a toy. Ah, to be a teenager, such a confusing time...)