Basketball is at best my 4th favorite sport, maybe my 5th behind soccer, so in an absolute vacuum, McDavid. That said, the impact of 18 year old LeBron on the mid-2000s Sixers would be huge. In the hypothetical where we somehow have a pick in that draft, and it ends up winning the lottery, we're looking at adding LeBron to mid-late career Iverson. Depending on timing, we probably don't end up making the Glenn Robinson trade, since LeBron would be penciled in for those minutes at SF. We would still be stuck with Keith Van Horn, but lets assume he's moved out for spare parts in the offseason. LeBron probably makes the team meaningfully better, enough so that we don't get Iguodala in the next draft. We don't need him for positional reasons, anyway. Let's assume we fall back far enough to draft Al Jefferson, instead, and we're looking at a lineup of:
Dalembert
Jefferson
LeBron
Wille Green
Iverson
That's a heck of a lot better than the spare parts the Sixers rotated through the PF/SF/SG positions in the actual timeline. LeBron probably runs as Iverson's Robin for the first couple years, we likely don't feel the need to trade Iverson in 06-07, as LeBron steps up and it becomes his team, with Iverson the second star and Jefferson a complementary piece. Most of our assets would go to finding either a solid partner for Dalembert if Jefferson remains at PF, or additional wings to allow us to run a small ball lineup with Jefferson at C, LeBron at PF, maybe Korver at SF, a SG (maybe we still end up with Lou Williams, he was a fairly low pick), and AI. Sixers might actually make some noise in the postseason during that time frame if we end up looking like that.
(Now, if I'm being stupid ambitious, maybe the Sixers, with LeBron and AI in tow, make a play for Shaq when he expresses a desire to get out of LA, something along the lines of Dalembert, John Salmons, our 2004 first, and some other spare parts (yes, I know that's not enough, neither is what Miami gave up), and we run Shaq/??/LeBron/Green/AI, and good luck to the rest of the league. But that's a bit out of the question for even this thought exercise.)