What's the best method between merging and rebasing ?

Hi,

Say I have a project in this state:

orig master -> A -> B -> C -> HEAD

I want to make A diverging from the original branch so I would be
at this state :

orig master -> A -> B -> C -> HEAD
     	    \
	     -> D -> E -> F -> 

I want master to be at  HEAD of the new branch and I want to pick
commits here and there from the original master branch.

How would you do that ?

I think I can't merge directly old master onto new master since
there are several commits I want to drop but what about rebasing
?

I guess I should cherry-pick interesting commits and rebase but I
am not sure.

Help would be greatly appreciated here :)
-- 
Xavier