I personally would go with the carpet pythons. They're attractive animals, make a great display species as they're prone to just hanging out on a limb in the open, and acclimate well to handling. Not to mention their care is pretty straight forward and simple. I currently own two carpets - a jungle X coastal cross male and a pure coastal female. However I just recently sold or traded my three others - a pure jungle male, a jungle X diamond cross female, and a pure Irian Jaya male. All three were great snakes, docile and easy to work with, not to mention beautiful. All of the carpets I've encountered are also pretty forgiving of husbandry errors. If it gets a little too cool or too warm, too humid or not humid enough, they able to tolerate that for short time periods until it's corrected.
Brazilian rainbows are considerably more sensitive to husbandry fluctuations from what I've read and are not forgiving with errors. You could easily lose your animal from not providing the correct care 24/7, 365 days a year. That isn't to say they don't make great pets, as I know a number of people who love their Brazilian rainbows, but they just aren't an option I would pick. As an aside, you might want to consider the Colombian rainbows. While they aren't as striking in color as the Brazilian cousins, they are never-the-less beautiful snakes with high irridescence. They are also a lot more forgiving of husbandry errors than their Brazilian counterparts. Here's a pic of my adult male Colombian rainbow (who's roughly 16 years old)....

As you can see, by adulthood they are a smooth chocolate brown with faint patterning and the irridescence is incredible in natural light (the picture with flash doesn't really do him justice). However as neonates and juveniles they show a very distinct brown on brown pattern that's quite lovely. I understand the Venezualian (sp?) rainbow is similar in requirements and temperament as the Colombians and also forgiving of some husbandry errors, though I have no experience with them.
Best of luck whatever your decision...they're all great! 
Raven