The #0331 from 2000-01 is generally considered the worst
Wrong. The 87-90 head, whatever number it is (686?), is the worst.
Furthermore, a head (or any other part for that matter) is only as good as the other parts around it. These parts all work in concert with each other and just swapping a head won't do much for you if you're not using a complimentary cam/intake/exhaust. The same can be said to all the people who think slapping a 99+ intake on an older engine will actually do something without a head/cam/exhaust to support it.
If you're building a custom 4.0 (or stroker) with all sorts of fancy parts, porting, polishing, the 7120 is the head to work with, but if you're just in need of a new head for your workhorse, it won't really make much of a difference.
0331 cracking issues? Way overexposed. The problem is real, but it is seriously exaggerated by the fact that people will log onto the web to say when theirs is cracked, but will never make posts advertising when there's HASN'T. There are a ton of 0331 heads out there that are just fine. Real problem, so always keep an eye on it, but just because you may have a 0331 doesn't mean you're fated for failure like people on the internet would have you believe.