I love this question and I love to answer it. And to answer it I think you have to look at two things and that is the element itself and the culture and nation behind it.
watching ATLA I always felt the most connection with the fire nation. I immediately connected to the will and desire that the people from the fire nation have - something I really see in myself as well. I loved the locations and characters of the fire-nation. The gender equality in the fire nation is great! and than the element itself which is beautiful. the most beautiful element. The explanation behind it, is why I like it but also because it just looks so beautiful. If you control it it means life but if you don't it is destruction. Fire is my number 1.
My number 2 has become the element of air , which became my number 2 later on. Aang is my all time favorite Avatar and one of my all time favorite characters, I connected to that character easily early on. The reason why I love air is not the element itself but more the culture behind it, the way of live, their traditions, their idea's of life. I felt sad that they were extinct.
My number 3 is earth, it was never an element I really loved, but at the fighting scene's I loved watching an earthbender, like Toph and Bumi. What I like about the earth Nation is that it always seemed such an indestructible empire and element, people who never give up and always go on, have hope. That's what I very much admire, - Facing your problems and fears head on. Though it is my number 3 for a reason I am tend to run away from my problems.
My number 4 and least favorite element is Water. Iroh ones said that water is the element of Change and that is a thing that is against my personality. Change can be good some times , don't get me wrong. But some things should never be changed.I don't like change and am more of a "Past-History-guy". Another reason I don't like this element/nation is that there is no equality of gender at all and no choice for marriage, meaning no freedom. What I love about this nation is the kindness and loyalty and love there is for one another in the tribe. than the element itself, I was never that much impressed by it, as the opposite element fire. And characters I disliked where mostly from the water tribe. ( No not Katara or Sokka).