single 7" Ls with light HE shells, if your BO/gunners can handle them. 

but then it may be different in May or June.....and omg February

For April I would go with any "A" series guns.

November I prefer "N" series guns.

December I gotta have "D" series guns.

And "L" series are good all year long.

you should go with single 7' Ls with HHE, if your gunners can't handle the accuracy you should go with single 7' Ns or D's with HHE...

dual 6's (any of those) are also very fun, but they kinda weight too much to use e'm once your crew starts getting fat. BTW use HHE since you need to punch hard DD/CL/CA in blitz or make the "OMFG 500 damage per shell against SS" in GB

dual 6" Ns/Ds with a few HE Light binds in A and 1 AP bind in B

The current available 6" have a reload time of over 4 seconds.

The DDX has been nerfed. What is the best gun now, any level, and Shells. 

Many years ago I had fun rocking a skele crew and dual 4" guns and packing on the belt.  Could bounce most everything at the DD level, just had to get in close and dodge torps.  But this was also many years ago.