I would think LeBron would say in the East just because he is guaranteed to make the Finals. However, if he went to the West, the Western Conference Finals would essentially become the NBA finals, so LeBron could go all out there, and then rest by playing 30 minutes a game in the NBA finals.
I don't think Lebron wants his legacy to be a 3-10 finals record, so the Western conference may be more appealing than we think. Part of Jordan's mystique developed because he missed the finals rather than lose in the finals.
Plus, Philly and Boston are going to make much harder for him to make the finals in the East.