I re-read the original post, and realised that I might have misunderstood the question somewhat. I'm very sorry. I still stand by my original comment in that I prefer to collect characters from my favourite stories rather than just toys.
But I sense that you might actually be asking; Do you like Transformers because you like the characters and mythology, or do you like them because you just like robots in general?
Well, I received my first Transformer when I was 5 years-old, and I saw that Transformer on TV, which excited me a lot. From then on, I was hooked on Transformers. Before that, the only interest I had were trains and locomotives. So no, I wasn't really interested in robots until after I got introduced to Transformers.
Several years later (I would have been about 8 years-old), my interest in Transformers dropped, and I became more interested in Superhero comics. Even then, my favourite superhero was Iron Man. Though he was just a man in a metal suit, he looked like a robot; like a Transformer! And that's why I liked him. Then as I grew into my teens, I became more interested in other superheroes like Spider-Man and X-Men, who weren't robotic at all. Then I became more interested in girls...
In my early-20s I became interested in Transformers again. It happened one day when I got really bored after university and bought a Transformer. I was so impressed with the design and engineering that I decided to buy another one..
Nowadays, as an adult (kinda sorta), I like sci-fi stories about robots and aliens because they all look different from humans; which makes it a nice way to escape from reality. Also, because the aliens/robots all look different (or the same depending on which story), you won't be reminded of the social problems we face as humans, like racism, money problems, etc; because those things don't apply in a world where everyone's a robot or alien.
Do I like Transformers because of the stories? Or because they're robots? My best answer: I started off liking just Transformers because of the toys and cartoons, then this love of Transformers made me appreciate robot-fiction more.. But still, the stories and characters are important to me, and plays a big part in my decision-making when I buy action figures.
Apologies for the long post. It's not an easy thing to explain. Perhaps there is no real explanation.. I just like Transformers