I guess it depends on how you want to describe "favorite". And how old you are!
In one sense, my favorite Estes kit was probably the WAC Corporal. I must have built ten of 'em. It was a great performer, looked cool, was reliable and cheap (important when you are a kid). It was also a (semi) scale model, which I liked.
My favorite Estes model to fly was the Scissor Wing Transport. I got one for Christmas when it first came out. Absolutely spectacular to fly. My family still remembers watching it circle down to a smooth landing on the "lakebed" (local school playground was all dirt, Kinda looked like Edwards if you squinted a bit and used your imagination...).
Of course we all fantasized about the Interceptor. I didn't even see one in person, built or kit, until about 1980.
We didn't really get much in the way of Century stuff in my neck of the woods, though the occasional catalog would find it's way into our grubby little mits. There was a sense of "forbidden fruit" about everything in there!
Good memories!