It depends solely on league format for me...
Zambrano is hot and cold... he will come out for 3 starts and blow away the competition and then his next 2 will be 6 ER head shakers. I don't know about you guys, but H2H i want someone solid who you know will give you 7 strong IP of around 2-4 ER baseball, with good Ks.
If we are talking Roto, then Zambrano is the great because you can hopefully sit him against teams you think will rough him up, with no immediate consequence.
As far as Bonds and Manny go... they are both aging stars.... Bonds, when healthy, is one of the best fantasy producers, and there is no reason to think that he won't put up numbers greater then or equal to Manny, but there is one exception... Bonds produces week in and week out... Manny takes the first 2 months off.... and H2H that hurts his value.... whereas again Roto, you can afford to sit him for a hot bat.
All in all, buy low - sell high strat is just as much a gamble as drafting in the first place.... there are always the players that make comebacks and the great players that take nose dives... just ask Todd Helton (1st rounder 2 years ago)...
At this point, I would think extremely hard about trading my Hudson/Bonds for his Zambrano/Manny... but if im in a H2H league, I'd probably go with steady production of streaky stars.
ETA: I think Hudson is back, and from watching his last 3 outings, I don't see him faltering back to '06 form. If he is pitching like he did in Oakland again... then Hudson > Zam in every cat except Ks... I'll take 3 cats to 1 any day. Plus Hudson has never been under .500 W/L in his career which is excellent considering how terrible he played last year... I think he is a good candidate for a 20 game winner this year.
"I never used a corked bat...And if I took it to court I'd win that case." --Albert "Joey" Belle