1. Expertise improves your dps. It just doesn't improve it as much as other stats do. So if all the rest of your stats stay the same, more is better. I'm pretty sure you know this and are just asking the question so someone will hold your hand and tell you exactly what gear you should wear. That brings us to:
2. Make your own gear decisions.
If expertise is the lowest on the stat weight does that mean I could have 7 expertise and still do the same damage per second as I do with around like 15 expertise? I’ve been looking at replacing my Heroic bone drake enameled boots ( 83 crit reforged to 33 haste and 60 expertise) with my blood soaked saronite stompers by doing so I lose 8 expertise which drops me to 7 from 15. I want to know if it is worth it to obtain all the extra haste from the boots and lose all the expertise.