With regard to defense or health you need to consider effective health (health x mitigation). Say you have 20000 health and 10% mitigation, that's 22000 effective health (20000x1.1). Do the math for your current stats and the options for your enchants to determine which is better. Life steal is another possibility, but it…
Crit vs. power has nothing to do with base damage vs. power. Bhem, are you spec'd into crit based feats/paragons? How are you determining you are doing more damage?
CWs will top the DPS/kills by being on adds anyways, the AoE damage is far superior to focusing a boss. There's no reason to say you have to do one or the other. I just hate it when melee thinks the CW can handle all the adds all the time.