Seeing as you're a Paladin, just follow this BiS reference when purchasing your Myth items.

I myself didn't upgrade my shield simply because I'm still praying to RNGesus for my Allagan Shield from T1. I was lucky enough to get my gloves from T4 so that's good.

In short, you'd want to spend your myth like this:

Hero's Ring of Fending -> Valor Surcoat -> Valor Coronet -> Valor Cuisses -> Hero's Bracelet -> Curtana Zenith.

If RNGesus hates you as much as he hates me, then go ahead and get Holy Shield Zenith. I still refuse to get it though as I believe in RNGesus.