"Spawned from recent post?" How about "spawned from 300 recent posts?"
I believe you've reiterated the single most asked question on the entire internet.
http://www.thehighroad.org/showthread.php?t=514751
http://www.thehighroad.org/showthread.php?t=515762
http://www.thehighroad.org/showthread.php?t=493241
http://www.thehighroad.org/showthread.php?t=500956
http://www.thehighroad.org/showthread.php?t=520114
http://www.thehighroad.org/showthread.php?t=452352
http://www.thehighroad.org/showthread.php?t=515720
There's seven recent threads touching on the question. Thousands more out there if you still can't make up your mind.
The basics...
AR-15: Direct Impingement gas operated rifle.
AK: Piston-driven gas operated rifle.
AR-15: Average 2 MOA accuracy with the capacity for much better.
AK: Average 3-4 MOA accuracy with the capacity for ... 2-3 MOA accuracy.
AR: VERY modular... the "lego" rifle. Build it however you want.
AK: Lots of aftermarket stuff available, but not as flexible.
AR: $700-$3000 +
AK: $350 - $900
AR: Somewhat fragile mags, but some good ones available.
AK: The toughest, most reliable mags ever... and almost every one works just as well as another.
AR: Pretty reliable -- not everyone believes it though.
AK: Very reliable -- everyone believes it, too
AR: Generally good ergonomics.
AK: You can probably learn to live with the ergonomics.
AR: Lots of caliber choices, but usually 5.56NATO.
AK: Usually 7.62x39mm or 5.45x39mm. Some available in 5.56 NATO
AR: Great sights, and easy to mount any scope for any mission.
AK: O.k.-ish sights if your eyes are good. Scopes that mount easily are eastern-bloc style and can be a bit funky. Alternatives can be had but they take work and/or compromises.
And so on. .... so
VERY on.
You don't need a book. You need to look at a few at gun shops, or ask around to borrow a few shots with each, and then ask more specific questions (or
do more specific SEARCHES) here to get the answers you're looking for.
In the end, they are both very capable combat carbines.
(Oh, and unless you are specifically buying a "select-fire" model that can shoot full-auto, the term "Assault Rifle" isn't technically correct.)
Good luck, and happy reading!