I have no experience with either the Crispi or the Zamberlan. However, two of my hunting acquaintances do. One has the Zamberlan the other wears Crispi. Both of them swear their brand is the best. What I have found is that boots are a lot like optics: 1) You get what you pay for; 2) When you finally upgrade, you wish you had done it sooner; and 3) preference is in the eye of the beholder.
When dealing with top of the line models from brands such as Crispi, Zamberlan, Schnees, Hanwag, Lowa, Kenetrek, Meindl (I'm sure I am leaving several more out) - it will come down to personal preference. Some have stiff soles that excel in climbing rock, while others have a more flexible sole that helps you 'feel' uneven terrain better. Each boot is cut different, so naturally your feet will feel more at home in one brand as opposed to another. Sometimes the boot is right, but the insole needs to be replaced for a better fit and more comfort.
I have never tried to compare warranties between the boot manufacturers, so I can't help you there. I suspect that most brands offer close to the same warranty as their competition. For me, I ended up with a pair of Kenetrek Extreme boots. Just like buying my first pair of Swaro 10x42 SLC's, it was a "buy once, cry once" experience. It was also one that I have never regretted.