Van Gaal should be your best choice, he was behind the great Ajax side of the 90's remember and almost led Bayern to a treble in his 1st season there. Begiristain doesn't really have that great of a track record honestly.. Zlatan, Caceres, Chygrynskiy, Keirrison, Hleb et al comes to mind.
I love Van Gaal. He was my first choice when Rafa left, but his stock at the time was at it's highest for 15 odd years. Those achievements came as a coach though, not a director of football. I don't think he has DOF experience. He was a technical director (we have one of those) and he left that, I think, because of disagreements (mind you, I think Van Gaal leaves everywhere due to disagreements).
Van Gaal strikes me very much as a training ground manager as well. I always get the sense that he spends a lot of time drilling his players tactically, which you would assume would still remain Kenny Dalglish (and Steve Clarke's) role even if Van Gaal was brought in as DOF.
Both he and Cruijff (
) seem really strange candidates because neither come close to filling to mandate that Comolli had.
Bergiristan on the otherhand had almost exactly the same sort of role at Barcelona, but was far more successful. And it is worth noting, that I think all of those signings you mentioned were Guardiola's choices. I think a comparison of his signings pre-Guardiola and post-Guardiola was interesting. Under Rijkaard you've got the obvious Ronaldinho, Deco, Eto'o signings, but also more left-field ones like Davids, Larsson and Gudjohnson who I thought did a really good job there considering the minimum fuss they were brought in with.
If we're simply replacing Comolli then he would seem a far more obvious candidate than either Cruyff or Van Gaal. I'd argue actually, for the sake of RAWK, that whilst he may not be keen on the position and it may do more damage that good, that Rafa Benitez is more qualified to do Comolli's job than either Cruyff or Van Gaal. After all, in Rafa's final season at the club he virtually took on that job, as well as first team coach.
If we're not looking to replace Comolli directly then there is more scope for seeing how Van Gaal could work, potentially. But that would in no way address who sorts out the contracts, the wages, the scouting etc. Neither Kenny or Van Gaal seem set out for that responsibility, and if you're giving it to Kenny you risk the exact same thing that happened with Rafa - he'll be spread too thin, trying to cover too many bases. ... Or to put it in Benítian "If you have a small blanket and try and cover your feet your head will be cold. If you try and cover your head you'll be left with cold feet."