Your choice depends on the effects/enhancements you are trying to achieve.
I favour IH2 because it does a lot more than just enable a "hover/zoom" function. It basically "rewrites" the images, cleaning and optimizing them in the process and creating "cached" copies which result in very fast loading of high-quality pics (the most critical element of any webshop).
Lately I've been looking at magictoolbox.com who've developed a variety of really nifty image tools. (I hope forum mods won't edit out this reference as they are commercial packages!)
I've "overlaid" a couple of their modules on a ZC install that already uses IH2, and I am getting the "best of both". Right now, I am still testing this (combination of magictoolbox and IH2) so I can't be sure if there are conflicts - but their modules are very sophisticated.
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PS: I have no commercial interest in magictoolbox.com, nor do I endorse their products. I just find them to be really innovative and that add a new layer of sophistication to a ZC install.*