No-one really knows. You can get Pierce at 10, Rondo at 21, or Michael Olowokandi at 1.
whoa!!! are they entering the draft this year??

but yes, your point is outstanding. having a better pick is, well, better. the ODDS of getting top talent increases the better the pick. having said that, koz is spot on that the draft is a crap shoot, even with #1. (can you say "anthony bennet"?)
indeed, i read somewhere, someplace, sometime, long, long ago (i.e. i am too lazy this morning to look it up again) the the #2 spot in the draft has the worst record among the top 5. the reasoning was that after the clear cut #1 pick, GMs often prayed and reached.
in this draft there seems to be 4-5 "sure bet favorites". after that, the next 6 or so are pretty much interchangeable depending upon your personal criteria, views, and team needs.
after the 10-12 spot, things get dicier. less talent is there, and more guesses and hope-fors and maybes appear. ("IF looney develops a jump shot, he can be a star sf!" sort of thing.)
if the celtics end up in the 12-15 range, unless someone drops, i expect danny to spend assets and trade up.