Emerald with the 5.25 RP10, no question. If you have high level reload gunners, it's an
awesome ship, though you'll run out of AA ammo quickly if you attempt to spam like an
Emden.

CL Emerald hands down. You could even add it a sonarman to help warn you of subs.

If you can, get the KM AA ships as an escort but only if you can spare crew to do so.

I use Emerald as my AA ship and escort..

Emerald with 4.5"/45 RP 10 Mark IV D and normal Reload gunners or same guns with
type A and AA gunners

AA escort ship (under AI control) equipped with Pompoms are ferocious - if for nothing
else a visual spectacle.... AI also alters altitude without a break in fire too :)

Emden, Z1, Z99...

Those guns, with normal Reload gunners. The escort that can mount the most of them is the
Emerald. It's faster than the Dido/Sirius and has more ammo capacity.

If you're unfortunate enough to have AA gunners instead, use the A version of those guns.
A bit shorter range, but they do the job at a better range than the pompoms.

5.3"/ 50 RP 10 Mark I