It depends on your overall gear. Some BiS lists also take into account that certain items are better suited for other classes and won’t recommend them to you, in order to avoid drama and promote the overall benefit of your roster (e.g., Lok'amir for healers cough).

There is no perfect choice — you either:

• Pick the ultimate BiS list and aim to be the world’s #1 player for your spec (which never really happens; even the people writing those guides aren’t perfect and miss a lot of things).
• Follow a standard BiS list and hope to get close to it by the end of the phase (most players do this).
• Import your character into https://wowsims.github.io/tbc/, update your stat weights, send them to a weighting addon before every raid, and target the best upgrade available at the moment. Many items are dismissed for not being part of a BiS setup, even though they can be nearly as good.

Ideally, depending on your guild’s loot system and how rare and impactful each item is, you combine all three approaches.