First off, you have to get what makes you happy. I have all three you're considering and as far as being satisfying and interesting captives, corns rank a distant.....distant third. They're just a tad more interesting than my BP's. This is how they rank with me...some people love both, while I find they pale in comparison to my Morelia.
Secondly, the behaviors of both Jungles and IJ's are similar, with my jungles being slightly more visible and active, but just slightly. On the other hand, my IJ's are more predictable with a calmer demeanor than the jungles if that's a factor. As for price, take your time, as you can find potential TROPHIES out there on occasion for very good deals (I've seen a couple on this site recently).
Lastly, I typically feed my females of both species an appropriately sized rat every 2-3 weeks, while the males eat every 3-4 weeks to keep them on the lean side for breeding. Most snakes are overfed in captivity, and Morelia are no exception. While you could feed every week, I feel yearling to adult carpets don't require it.
Hope this helps.


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"He who would stifle debate rather than engage in it, does so at the expense of his integrity and credibility"
Mike Curtin