I think The Blue Spirit, The Storm, and the finale episodes are the best of Season 1. Season 2 basically everything after The Blind Bandit was fantastic. Season 3 I think Avatar and the Firelord and everything after Nightmares and Daydreams were awesome.
I don't remember what hooked me, but I do remember Avatar being a guilty pleasure of mine. It came out when I was in 6th grade and by the time the 3rd season rolled around I convinced myself that I was too old to keep watching it so I don't remember ever finishing the third season. I have since done so and I now realize that you're never too old to enjoy a good old fashioned cartoon. Childhood ftw.
That would be a cool fight. Toph is the greatest Earthbender, and if I remember correctly she only has lost to Aang. Terra's powers can cause natural disasters. Toph wouldn't have any problems with projectiles, but since Terra doesn't use bending and instead more of a telepathic control, Toph loses a pretty big edge she has on any Earthbender meaning her ability to 'see' their attacks before they even come. I'll pick Toph, I feel like she is the better fighter and she has such a mastery of Earthbending.