I have a hard time figuring out which 20" AR is my favorite, but I guess I like all the ones I have for different reasons.
I have three A1 clones and they are just cool. Nice, lightweight and simple, the way ARs were supposed to be.
I only have one A2 clone, I love it for nostalgia. The A2 was what got me into daydreaming about ARs and wanting one in the first place. I might put together a second one someday, but probably with an A1 profile barrel.
I don't really have a true A4 clone, but I have 3 that are
my take on the A4. One almost could have been a perfect copy of an A4, but it has an A.R.M.S. folding FSB. The other two have fixed FSBs, but they have A1 profile barrels.
If I was really pressed to choose a favorite it would probably be the lightweight barreled A4s. They just feel the best in handling and the fact that I can put an ACOG on them is nice.