How should I evaluate the suitability of acquired equipment in Diablo 3?

I am having trouble figuring out which equipment is worth using when playing the main story line of D3.

I found a shield for my Crusader character which looks much better than the one I was using: the rating is higher (714 vs 547), also the Block Amount is much higher (948-1088 vs 392-543). It also has a marginally higher chance to block.

However, the game shows me that both my Toughness and Recovery will both be diminished after equipping the new item (by -12.1% and -17.2%, respectively).

I often find myself in a situation when the rating and the raw stats of an item look like an improvement, but the stat changes calculated by the game show a (sometimes hefty) decrease.

What is the cause of the (apparent) discrepancy, and which set of values should I trust. Should I equip the shield or not?