Since you asked in this thread, I'll answer in english^^
I get Pippin at the very beginning or I don't get him at all.
As said above, I tend to recruit Beregond quite early, even before I get archers or pikemen.
Boromir is a hero I don't get every match, soo... usually when I'm around/above 1000 CP and I expect some big fights where I need my melee fighters to tank damage. His leadership synergises best with tower guards when they use their formation (actually, swordsmen as well) and archers deal the damage from a distance.
In case there are some enemy heroes I cannot deal with I prefer rangers over Aragorn. And since I like using rangers, I very rarely go for the king^^
Gandalf is recruited even later than Boromir, especially when I'm fighting big clumps of infantry. Well, classic lategame hero... just get him when you have the money^^
Faramir is kind of special since he is not recruited in the citadel. Most of the time I recruit him when I already have ~three ranger units on the field.
Remember though, this is just my personal opinion and playstyle^^