Hard to say without knowing your full setup.

There's also a possibility for act 1 faith mercenary.

You reach max attack speed (9 frames) in regular situation, and 12 frames when decrepified (that happens a lot in Chaos sanctuary and Baal throne).

Fanatism would allow 10 frames when decrepified, with slightly better attack rating and damage + 144%.

Might/Pride mercenary is a brutal boost of ~ 550% damage. Get CoH on him for +2 to might (fortitude is pointless here).

Both have +/-, I think they are equally useful (act 2 mercenary is better to finish off Baal/Diablo themselves, if you feel losing time here).

Notice that 15ias/40ed jewels in both helm and shield would get you at 11 frames when decrepified, without Fanatism, and 9 frames with fanatism.

act 5 merc with ber/ber coa, ber guardian angel, lawbringer phase blade

jospa nyt vaa testaat sitä a5 lawbringer nii tiiät jo mikä on paras

i have found lawbringer merc to be the best for a tele zerka papa. go with that imo, it's cheap af and effective. ber ber coa ber GA like goomy says should be damn near indestructible.