I have eight 4 or 5 star shields now and the one I go back to again and again is Grey Owlite. Places where I need to shield tend to either have lots of elemental (arena bullet hell/20 mech knights) or lots of fire (FSC or Tier 3 Gremlin Scorchers). I've tried, can't beat that shield.

Elemental, shadow and normal are all useful. Probably in that order. UVs don't add a ton of defense to your shield, especially compared to the amount of defense it already has. Someone recently tried a low vs max UV on a 5* plate shield, I think the max broke in 12 hits, the low in 11 hits from a jelly cube. Wish I could find that forum post, darn you search!

In my mind, the ultimate shield would be a Grey Owlite with the max shadow UV. Being able to soak up hits from T3 undead and fiends is pretty nice. Fire resist is pretty nice for pushing through the walls of flame prevalent in T3. The dragon scale shield could be nice too but I think it'd be strictly a T3 implement. I think most of the utility in a shield comes from being able to bounce stuff or survive multiple small hits.

I also read the post that Culture is referencing. Yeah, the enhancement for defense UVs on shields appears to be less significant than helms and armor.