No offense to some of these kids, but I would not draft some of these guys (Giles or Jackson). If Jackson goes, that's a big mistake. He's not ready and there's a good chance he won't be drafted in round 1. I think it's a mistake for Giles to go as well.
Giles turning pro is not about a "dream to play in the NBA" - it's about getting a contract by being drafted in round 1 because the only way he makes it in the NBA is if he gets fully healthy - which will take a year or two. He won't be doing anything next year but sitting on the bench. But, as far as development is concerned, his best bet would be to come back to Duke, get fully healthy, and become a better basketball player. Giles best chance is to go to a team like San Antonio and be given a couple of seasons.
On Jackson, if he were to declare his best bet is to not hire an agent and see how he does at the pre-draft camps. Then he can get an idea as to whether he will be drafted or not. Giles also should not hire an agent, imo, because he may not do well at those camps (if he goes to them).