When i was first starting out, i did a lot of research as to the different varieties that i could legally hold in captivity. I ended up buying a juvenile coastal carpet python (morelia spilota mcdowelli). Then that was it, i was hooked. A month later i bought a juvenile JCP (morelia spilota cheynei). The following are my experiences...
The jungle was (and still is) a gem. She would eat on command, and never give me any trouble.
The coastal entailed a different story. After i bought her, she went 25 days without food. I ended up giving in to my preconceptions about feeding live (stupid morals that i have) and finally got her to eat one live, after it stayed in her enclosure for 2 days. After that, she would eat once every 3-4 weeks or so (frozen/thawed), and believe me, it was very stressful on me as a new owner. Eventually, she grew out of that and began eating once a week.
That said, the temperaments of both the JCP and the Coastal Carpet were fantastic. The jungle, to this day, has never even put herself in an agressive position. The carpet will often get a bit defensive, but has never struck at me with an open mouth.
But, a recommendation to you, whatever you buy, buy it as a juvenile. That way you will have a long time to, as said by other posters, 'grow with the snake'. Keep in mind that carpets are slow growers. Anacondas are not. Within a year of buying an anaconda, you may have something that is totally unmanageable to a new owner.
Well, I suppose that the moral of the story is this... You should find a snake that you really want, and, provided it has a good temperament, buy it. Just don't buy something that is going to grow too fast. And don't settle for something that, in your heart of hearts, just isn't what you want. With enough attention and effort, most snakes can make great 'pets'. Dedication is the key.
Also, just a query, how old are you? Do you live with your parents? And, do you have an income? I'm not asking to sound condescending. The reason is that, after the initial costs of buying a suitable enclosure, snake, and a couple of frozen rats, the dollars don't cease demand. Weekly rats are going to cost you. You also need to have enough money to pay for vet bills and medication in cases of necessity.
Hope this helps, and happy herping. And, my apologies for the lenth of this scatteringly long post 