Chad Ford today with a good article, succinctly (if not particularly original) balancing the old 'talent vs. need' factors:
He then uses a speculative Bulls draft board as an example:
Team needs: PF, C, SF
5. Corey Brewer
6. Jeff Green
1. Spencer Hawes
2. Joakim Noah
3. Julian Wright
4. Al Thornton
If the Bulls are drafting No. 9 (Tier 3 territory) and Corey Brewer is on the board (a Tier 2 player), they take him regardless of position. The rule is that you never take a player from a lower tier if one from a higher tier is available. So if the Bulls had Spencer Hawes ranked No. 1 in Tier 3, they'd still take Brewer, even though center is a more pressing need.
That's pretty much how it should go. Of course, the very subjective portion of this is where players fit in 'tiers' for each team. For my selection in the SBNation mock draft both Hawes and Green were available, but I (using Chad's terms) had them in the same tier, so I took Hawes. If the Bulls believe that Green is that much better, then I won't bemoan the lack of the 'need' pick.
[Oh, and quick aside to the Kobe & KG discussions. Lets all assume for the sake of (non) argument that if one of these guys are acquired, the impending opt-out clauses in their contracts would be negotiated away as part of the deal. Naturally there will be no trade for a rent-a-star]
[Another aside: the SBNation mock draft is nearing the end of the first round.]