I am level 96 whirl wind barb, I have max whirl wind, battle orders, battle command and mace mastery. I would like to know what skill is the best for me?

You only need 1 point into battle command. Could max shout instead.

Assuming you have a maul or something.

Beserk helps against physical immunes and helps if have a physical breaker sunder charm.

20 sword mastery (cuz you’re using 2x grief pb, right?)
20 ww
20 bo
1 bc (not 20)
1+ shout
1+ zerk (unless you use a reaper merc)
1+ increase speed
1+ natural res
8 other points in prereqs (howl, bash, stun, conc, leap, leap attack, stamina, iron skin)

You can then either add more to your liking into the 1+ skills
Or
Dump pts in find item/potion if you care about using it for extra drops

I am using IK set

So you already have 20 base Mace mastery as you mentioned earlier. I also concur not to max out Battle Command, just 1 base point as you get bonuses from All skills and Barb skills using the set.

+1 base Berserk skill comes in handy and increased with IK set bonuses and other gear (ammy if using Maras, Highlords, Seraphs etc)

Check your Resistances and improve by either Skill or Inventory items.

Increased speed is based on FRW and encumbrance penalties with Heavy items, and IK set is mostly heavy items, so movement speed may be slower than normal. ... check movement after gear before adding any points to it.

Shout is for more Defense, also check if it is a synergy to another skill you are using.

Good luck and have fun.

Yes, max 1 battle command.

Find item can be skilled if you want, 1 berserk is mandatory i would say to deal with immunes.
If it feels squishy 1 war cry can be fun for stun.

Hey man I have a pvp bva post about barbs it could help you out.