In my opinion, all the BC-BB's are good setups for AA.  The Dland is better than the Hipper/Eugen class but the guns are the same all the way through to Kaiser.

Either the 5"/61 KM 40 (Golden Angle 32) or  3.46"/76 SK C/32 (Golden Angle 36) will do you well. 

Dont try to mix and match on ships that have different sized gun slots.  Go with one gunset and with good RF gunners, you will be a potent threat.

Everything you need to know is in this guide:

http://www.opennavyfield.com/smf/index.php?topic=421.0

what the above guy said. Also responding to your qauestion, go with Emdem o PCA, it's up to you. The guns and GA are on that site But I highly recomend you to stay away fro the 36 degree guns. You can mix AA guns as long as the Golden Angle is the same. That means, you can have the 5" KM40 along with the 4.1" (I believe this is the gun size, not really sure, it's been so long since I used AA). Hope this was helpful.

P.D: Higher golden angle=Shorter range. 

For pure aa emden or moltke.

At higher level tho the emden cease to be an option: I don't think I can fit my fatty crew in it any more and exp wise you will use a moltke if you have one, no doubt.

I'd say emden with 4.1"

You get a good ammount of ammo and a ton of guns to spam shells with and even with bad accuracy SOME of them should hit.

Or a Opro with 4.1" and 5" in the two big slots.

The GA difference between 4.1" and 5" is 1 deg but it barely matters in terms of AA and you are virtually guaranteed that you never (at least in a normal GB room) run out of ammo.

Or you could just get a Moltke sell the main guns pack 3.5" in the t slots and go wild OHing 50+ knts and spamming flak everywhere.

Ppro1

It levels faster than moltke, we're talking about blatant bugg denied by SDE.

Better AA, emplacement, and you're unlikely to run out of AA, at least, not frequent as moltke.

Easyy to hit speed cap.

Possible to get for those that do not do online transaction.

I think that KM AA ships are 2, with different features each one.

Emdem: Have 8 slots ans you can fire 6 to each board side at the same time. As the slots are better distributed in the ship can cover more area, but deal less damage in the same are. As those slots are the main ones, when turns the ship have to re. position your guns to accurate fire. It´s also a relative weak ship compared to Molkte

Moltke: Is a strong ship, and as concentrate all guns in mid ship zone can wipe out a full DB´s wing in seconds. Also, have son extra slots to put HH, just to help chase enemy SS.
Also, as AA guns are un R slots can shoot even you are turning. This is a helpfull characteristic.

I tried 3 guns, 3.46", 4.1" and 5".

The 5" if the most lethal, but guns and ammo use a lot of space, so I switch to 4.1 some time ago. The GA is almost the same as 5", I try 0,5 degree up from 5" GA and works fine. 
The best feature of 4.1 is you can load a lot of ammo, that is helpfull passing 7 minutes of battle.


 

Best AA ship:

Moltke with KM-40s on r-slot

Hipper/Eugen/M-Pro are good to but less crew slots, no engi as BO and slower