"After watching Cory in The House, I was hooked on Animu."
First Anime I watched from beginning to end was Deathnote. I liked it a lot. I never thought that, what I'd thought were cartoons at the time, could have such real-world elements. Avatar: The last Airbender was the only cartoon that actually had details like that, but even it had elements from the east.
I'd seen anime on t.v as a kid before but I felt like it was something I shouldn't be watching. When I was around 9-10 I saw Fma appear on Adult Swim (I thought Cartoon Network was still on) one time and there was a lot of blood and fire. (thanks Mustang) And I was so scared I didn't watch much.
After watching Deathnote at an older age, I googled what I could watch next. Got into the big three, and binged some others. Hunter x Hunter, Fairy Tail, Attack on Titan, Akame ga Kill, and so on. Fma Brotherhood too of course (honorable mention).
If I had to pick a favorite though, for me it'd be Hunter X Hunter hands down.