Tommy4Ever,
I agree that "best AAR" is subjective, but I have some recommendations I posted in my AAR a while back that I'll post here.
I'd also like to amplify some of the comments above -- agreeing on Explorations in Strategy, A Special Providence, Director's HistoryPark series, History of the White Eagle, Timelines, Advantages Without Obligations, Eagles of Avalon, the Fu Manchu series, etc. I'd probably agree on some of the others too, but since I haven't read them I would have trouble recommending them with confidence.
Here's my post:
To make a list of AARs that I could recommend, presuming you're looking for fiction writing, not gameplay, there are some that leap to mind, though I know there are also two or three others which I should recommend which I'm not going to remember. There are some magnificent writers here!
Here is a list of great AARs off the top of my head:
Stnylan's
In Memory of France (not included first for no reason -- this is a GREAT work!)
Coz1's
Into the West and
For the Glory of Persia
Director's
A Special Providence (I think I may even be missing Director's best work -- this is the only one I've extensively read)
RossN's
The Patriot's Sword
FJ44's
Dawn in the East
The Yogi's
The Eagle and the Lion and
Empire of Fu Manchu (TheYogi has lots of great writing -- pick any of them, because I'm not certain these are his best -- I also can't remember which ones, for sure, I've read)
Draco Rexus'
For King and Country
Another I would add is CatKnight's Resurrection/Rebirth of USA (EU2). Many people really like TheYogi's Iron Crosses (HOI 1) too, and I'd agree (that's 4 TheYogi AARs I've recommended!).
If you're into politically-heavy storylines, there's also Estonianzulu's
The Footsteps of Illustrious Men (Victoria) and Sir Humphrey's
Sacred Grove of Brittania (HOI 2). Mettermrck's Advantages is also heavy on politics.
Two "sleepers" I want to mention --
The War Hero and the Presidential Election of 1948 (HOI 2), which is full of politics, espionage, intrigue, romance, etc.
The Last Mission (HOI 2) has deep philosophy, politics and romance.
And even after all these posts, we've probably only mentioned 30-50% of the "truly great" AARs. There's more out there. Just look for the other "best ever" threads and you'll find a good proportion.
I'm sure I'm still missing a dozen or more that I would highly recommend.
Rensslaer