I use HH prmiums. They require the least weight, both in armament and sailors. You can either use a sonarman or an escort ship to detect the presence of subs. Use auto aiming FCS to ease the quick firing of the hedgehogs.This is my opinion.

I haven't used anything up until now on the Arc Royal.

you "could" just run an escort AA ships (toss on a Sonar Sailor on board to help you spot incoming subs), then use your HH as needed.

however, I've also seen, and used your gun slots to hold support sailors,  especially repairmen or restorers, or to hold other pilots you're training up until you get more support slots to house them in on higher level cvs.

When I used to have extra displacement on either illus or ark, I slapped on the 4.5" guns. The first batch mind you.

Most often, I was reduced to using premium HH to shoot at subs and other annoyances. My gunners (110 at the time) got too heavy to use with anything but HH.

Also, manual FCS (Aiming) is preferred for increased accuracy while shooting. Maximum distance is achieved with the HH at 35 degrees.  You may need to learn the angles so you don't waste the expensive HH.

 You can leave your R slots empty and level another pair of pilots on the illus. When you reach the Malta (CV-5), you'll be happy you have either more fighter pilots or some offensive power.

 

I am currently in a PCV, and I still use my gunner slots to level up my pilots.  On smaller CVs with less than 8 support slots this is pretty important.

You'll want your max 8 pilots to be levelled up nice and evenly so you can use the next tier planes with all your pilots. 

In probably 5% of games I wish I had AA/HE to shoot. 7% I wish I had HHs. All other times I am glad I used that slot to help grind up two more pilots.