The claw will lower my HP with a single exception (a 19 cons necromancer) so for me it is a choice between having more HP and taking damage and having less HP and avoid damage. It is especially good on mages in BG1 where it hinders missile fire from disrupting spells.
AC is interesting in that a little can have a large effect. If the enemy must roll 10 or above -1 to AC is practically without effect, but if it must roll 19 it means a lot - changing the probability of being hit from 1/10 to 1/20. This makes even marginal improvements in AC desirable.
The eternal question is whether it is better to concentrate AC in one char or spread it around. It would depend on if the enemy is mixed or uniform groups I 'spose.

To bring this back on track - are there any items that will replace the helm apart from the claw?

On the material side, I'd say that the Buckler+1 can't hold a candle to Kiel's Buckler: Kiel's already is +1 for any character with a DEX in the 14-17 range, and is extremely important for Dualed Thieves (of which BG2 has no shortage), who need that precious extra point of DEX to boost the Thieving skills that they can't point points in any more.

But what really irks me is the way that BioWare jacked all the Bucklers in general: There are three classes (Thief, Bard, Druid) that are restricted to Bucklers, and yet instead of creating more decent Bucklers to sprinkle around the game, they decided to delete the only BG1 Buckler that was any good. And on <u>top</u> of reducing the Buckler selection to the +1 enchantment, they put only one Buckler in the entire game.
Rather unbalanced, when you look at the Sentinel / Fortress / Reflection / Harmony / Saving Grace / Dragon Scale / Balduran side of the equation.

Thankfully, Rogue Rebalancing rectifies this. Bucklers of up to +3 enchantment are available, Kiel's is back, and new custom Bucklers for Thieves, Druids, and (sort of) Bards. Yay!