who make hp interesting? villains or heroes?

Both. The villains bring the drama and suspense to the story and the good guys bring the trials and suffering and beat the crap outta the bad guys.

I also think the "anti-heros" (Like Severus and even Draco) make the story even better.

They both do, but if I had to pick, I'd say the villians. I loved learning about their back stories because it makes you think about how normal people can change so much because of an experience. Voldemort never had love, Snape wanted to find a place to belong, Draco wasn't treated right. It's so complex and amazing, and I love anti-heros.

Although, the heroes are awesome too, but we can't have a story without an antagonist.

That villains were more exciting to me. The heros were kind of boring as opposed to the eccentricity of Bellatrix for example. I love extreme characters. The villains seemed to deliver that to me more. I do like most of the good guys too, but as for them being more exciting, I would have to say no. There is a different reason why I love some of the heros.