Armor and resistances function exactly the same, but at a 10:1 ratio. That is, 10000 armor will reduce damage exactly the same amount as 1000 resist all. The thing is, they are both on a logarithmic scale, which means that there are significant diminishing returns at work. As a general rule, for maximum effectiveness you should concentrate on raising whichever one is lowest, assuming you have any kind of gap. That is, if you find a nifty new item while you have an armor of 12000 and a resist all of 1189, you can afford to gain or lose a few points either way, so you have the luxury of letting the other stats on the item guide your choice. However, if you have a wider discrepancy between the two, you might want to first see how switching out this gear will affect your damage reduction.
Oh, and when doing the above, don't forget to add in 1 point of additional armor for each point of STR/DEX the item gives you, or 1 point of resist all for every 10 INT the item gives you. The reason my Wiz was so tough even with such a low VIT prior to the expansion was because he was selecting items that rolled armor, INT and STR, which is how I was able to have a level 60 wiz with 12000 armor to go with his 1800 or so resist.
That's a Crusader, all right. They're tanks, through and through. They can gain armor like no other class, and they can wear a shield while doing it for even more armor. The Crusader class was created to use a shield, so if you're not using a shield, you're going to be rather limited. It would be like playing a Demon Hunter who doesn't use a bow.
--Patrick
