Must admit when I saw that you read that Cid shouldn't have used a spear, my first idea of an alternative weapon was a gun. I suppose I was thinking of how fighter pilots used to (probably still do) carry pistols around with them. That and it's a mechanical weapon, I suppose.

However, I think spears did suit Cid. There's the fact that Cid is - by and large - a Dragoon and also that I've always associated spears with wind, air and the sky which is fitting. Then there's the design of the weapon in Advent Children which - as mentioned - just seems to fit Cid.

It would've been nice if they'd made use of Vincent's claw, but I always thought it was simply decorative.