Chilling Armor provides roughly +70% more additive armor than Shiver Armor at level 20, but if you are going for Chilling over Shiver, keep in mind that the higher your Defense becomes, the less often you are actually hit and the less often your spell procs against ranged mobs. So it is arguable that Chilling Armor's ability becomes less useful as the level and gear quality increases, making it just a primarily defense-boosting buff. Keep in mind too that Chilling bolts do not pierce, so you have limited control of who actually gets hit.
I am personally a huge proponent for Shiver Armor because of how it procs on enemy melee attack and not enemy *hit* like Frozen Armor or Chilling (although generally Frozen Armor tends to outperform Shiver in actual practical playability). Yes, you lose some protection against ranged attackers, but the number of melee creatures far outnumbers the number of ranged ones in most content.
There are pros and cons to each skill, but you also need to keep in mind that in endgame, the difference between the two and overall impact either skill will have will only go down as everything else in your build improves.
So while Shiver > Chilling imho, the real answer to which you should get on your prebuff ES staff is whichever one you can find, then you account for the cons of that skill later. Unless you are trading or hero-editing, beggars cannot be choosers as to what actually drops for you.