If you have the opportunity, play with some snakes and see which ones appeal to you.
The two main options are: 1) Antaresia, all of which are all about the same size, all the same to care for, all the same in terms of behaviour, they just look a little different. Some people will tell you there are significant differences between them, and after decades of working with literally thousands of them, I say no. Individuals vary but not really species. Spotted Pythons are a little larger and some lines (as opposed to species) feed better than others, but as species they're all similar with a similar range of temperaments and feeding response. Blonde Macs (a type of Spotted Python) are among the best feeding Antaresia, but once established they're all good.
And 2) Carpet Pythons. These vary a bit more in terms of size and temperament. They're all much larger than Antaresia, most feed well, most are pretty tough (Diamonds are the biggest exceptions there), most are pretty good handlers (some lines of Jungles are exceptions and Darwins are a bit mixed).
The other option worth looking at is the Woma, which is a medium sized snake and about the only option significantly larger than an Antaresia but significantly smaller than a Carpet. They're good looking, brilliant feeders (SA Womas can be a little tricky as youngsters, but the others are very enthusiastic) and usually handle well other than their strong feeding response.
Other options are venomous, very large (eg Olives) or more difficult to keep (eg Chondros). Maybe Water Pythons deserve a mention. They're about the same size as Carpets, tough, easy to care for, great feeders and very beautiful, but they have a partially deserved reputation for being snappy. If you get a good one it's the nicest snake you could hope to own, but if you get a snappy one you're either a very good handler or you'll get bitten a lot. I've kept a fair few and bred hundreds of them and all but one of my adults have been excellent handlers, but there are some nasty ones out there. For me personally these are the #1 Australian python because they're such lovely, alert, aware snakes (Carpets etc just seem so dull natured in comparison), incredibly beautiful and very different looking from anything else available in Australia with their patternless bodies, amazing iridescence (check out some of the pictures I've posted on APS if you like), but preferences vary and these are certainly not very popular.