I have been told time and time again that nothing beats a diamond or murray darling carpet python for temperment. I have been researching nearly any snake you can possibly think of for about 2 months now, as im buying a snake in the very near future. I had the same dilemmas as you have, cage, type and prettiness. If you would be happy with a smaller python to sacrifice for colour, i would go a ball python in one of the many colour morphs they produce. Or if you want a bigger python, like your carpets, i'd go a diamond (which mind you grows to an adults size of approx. 3m) as you can get them in various colours, such as black and vibrant yellow.
As for me, i have finally decided on a murray darling carpet python as i believe they are beautiful and graceful and really well mannered.
To start off my reply, ball pythons are illegal in Australia and are not an option if you live here. all three options you are considering can be awesome first snakes, jungles can have fantastic temperaments, but can be a bit nippy as juveniles, the nippy juveniles often calm with age and you can ask the breeder about the parents temperament for a reasonable idea of what your snake will be like (there are obviously exceptions) this snake is good for beginners in my oppinion becasue these infrequent tiny nips will prepare you a little for the bitey side of owning snakes (you will get done at one point or another in my oppinion, no matter what snakes you have) and then they will usually calm down and be fantastic pets before they get to the size where the bites start to hurt. tend to suffer from "little man" syndrome. The smaller their adult size, the bitier they tend to be, but the bigger they grow the more placid they tend to be, even as juvies, you can get a pretty good general idea about what size they will be and their temperament depending on their locality, a bit of research will go a long way with this species as you really have to know what you want in a snake and the different localities of JCP vary so much in size/colour/temperament.
Diamonds usually have fantastic temperaments (again.. there are always exceptions) but can have more difficult to adhere to husbandry requirements and i would reccomend these snakes to beginners because these snakes really help you understand how to set and maintain temps, propper day/night cycles and all around attentive husbandry. other snakes will seem a bit easier to keep in comparison. they are a beautiful snake and one of the most popular snakes with more experienced herpers as well. They are at risk of developing Diamond Python Syndrome a disease specific to diamond pythons (perhaps not) that serpenttongue on this forum has some great information and introspection on and has posted a couple of threads on. because of this, even the more experienced keepers can have their diamonds die at a reasonably young age for snakes.
Black headeds (the one i have never owned) are good because there are smaller and larger varieties, much the same as any other snake. but the difference being 1.1 meters all the way to 2.5meters as fully grown adults. they can have good or bad temperaments in their cage, but have a bad reputation for being cage defensive but i have only seen one bloke ever bitten by a black headed and it was in feeding response with a rat in the enclosure. tend to be picky eaters as juvies but once feeding, tend to feed very well and have an insatiable appetite. in the same family are the womas, which tend to be a bit smaller and have an orage (yellow) head. feeding tends to be easier and they have a ferocious feeding response and once out of their enclosure are much the same as black headeds, if not a bit calmer. do not want to get bitten by one of these as they tend to latch on and it can be very hard to get them off. these snakes are great for beginners as they get beginners used to signs of snake behaviour. i personally find that aspidites are easiest to read in terms of their mood. they also tend to be good handlers, good feeders once going and can be selected to only require small ammounts of space.
LOOOONG post!
all my oppinion based on my experience and those of the people i have had lengthy discussions with, disagree if you will people with more experience than i, and i am sure there are plenty out there.
Razeunit - it is also pretty widely accepted that the UV thing is just a myth. but having said that i still advocate for it, because until i know what exactly causes it, i will fork out 120 bucks every 6-12 months for the security. although i dont have to do that now, i still have UV in one of my enclosures and am getting a second and third with UV in the not too distant future. because a bit of uv here and there cant hurt so long as you provide shade from it, also helps with day/night cycles i find.
