There are several great cameras in Canon's current line-up and it's hard to pick outright winners. When deciding which camera is the right one for you, it's important to consider your level of understanding as well as your current and future requirements.
The Canon 1DX is a superb camera, but it is designed as a tool for experienced, professional photographers. Its extensive array of controls are likely to be intimidating and confusing to the average novice photographer. It is also large and heavy, making carrying it a bigger issue than a smaller model such as the EOS 100D.
However, up-market Canon DSLRs aimed at enthusiasts are still usually very beginner-friendly, so you shouldn't let worries about complication affect your buying decision to much, even if you're a complete novice.
If you are a relative novice interested taking photography more seriously, an enthusiast-level camera may suit you better in the long-term.
Enthusiast photographers looking to upgrade need to consider their lens collection when deciding which camera to opt for. If you have a collection of EF-S lenses, which are only compatible with APS-C format cameras, then the Canon 70D is likely to be a more attractive option than the full-frame Canon 6D or 5D Mark III. If, however, you have a few EF (full-frame) lenses in your bag then a full-frame camera could be a good choice.
Full-frame cameras have the edge for shallow depth of field for effects, for example when you want to blur the background of a portrait. Meanwhile, APS-C format cameras are great for action sports and wildlife, where the crop factor of the smaller sensor effectively gives lenses extra reach.
The Canon EOS 700D stands out as the pick of the crop for beginners, with its excellent performance and clever features.
Moving up to the enthusiast sector, the 70D has largely overtaken the 7D in terms of features and overall performance. For our money, it's the best Canon APS-C camera of all time. If you're after a full-frame camera in this sector, the 6D is the full-frame body to go for, although it's worth seriously considering spending the extra on a pro-spec 5D Mk III body.
For a fully professional camera, the 1D X is not only the best Canon body, but arguably the best that's currently available from any manufacturer. The only sticking point is the price. On a less extravagant budget, the 5D Mk III is also a spectacularly good buy and a popular choice with professionals as well as advanced enthusiasts.