Which L!Ike IV's?

It really depends. Neutral Ike has less speed, but more resistance (which is arguably L!Ike's worst stat) while the other has more speed to prevent doubles from SOME units.

Out of the two, I'd use the +Spd L!Ike.

As far as who likes Warding Breath, that's a bit difficult since Steady Breath is much better on 95% of units, and you can't give it to someone like Felicia because she's ranged.

I'd say give it to someone that's either a Mage-bait specialist, or someone that has a balance in defense and resistance (like Sheena, or maybe even Gwendolyn).