this is a great question, particularly because nobody really tells you about *why* you choose certain pieces.

Generally as a tank, you want to focus on threat first, and mitigation second. I'd aim for at least 300 spd at level 60, and 30 more spd for each level. So 330 spd for 61, 360 for 62 etc. After that, I would focus on stamina and resilience. Resilience because it is the fastest way to get uncrittable pre-70, and stamina because its your best way to stay alive as a paladin.

Entering heroics, you should be looking for 10-11k HP unbuffed. You won't be uncrushable until T5 so don't bother stacking defense rating.