How you prioritise your stats as a Tankadin depends largely on the content you're tackling. For normal mode raiding, I'd go for a high control / steady damage intake build, which means:
Cap hit (7.5%)
Cap expertise (15%)
This gives you a good rate of HP generation, leading to smooth damage, as opposed to the spiky damage of an avoidance-heavy build. Speaking as healer and raid leader, I wish all tanks took damage as consistently as a Paladin.
If you need more advice, our main tank Danatheron will be happy to help, just give him a /w.