Angular should be noted as AngularJS.
Angular 2 should be noted as Angular.
Angular 2 should be noted as Angular.
My org has been dealing with Angular and AngularJs for the past two years and developers and non-developers alike get confused or unclear all the time when we try to communicate about the two. The only thing that's been successful has been to describe them as "Angular 1.x" and "Angular 2+".
On top of that, when doing searches for documentation and issues, it's still absolutely necessary to add "2" to searches for the right version of the framework.
It would have been a lot easier on the world if 1.x was the last version of anything called Angular and Google named the new thing FooBarJS.
But Google knows how software teams work. Names and versions are easier to evaluate than trying things out or running comparative analysis.
Teams hire "Angular" developers which usually means "1 or 2" even though it very much shouldn't.
Teams will set aside time to "upgrade to Angular 2" more freely than they would set aside time to "switch to a different framework, FooBar.js", even though with Angular 2, those are the same.
Even if teams would set aside time to "Upgrade to new framework", they're much more likely to do a alternatives analysis if it's not just a version number changing.
That said, I think this hurts developers and teams, and I think it's loosely nefarious, but it was probably necessary for Angular 2 to get the adoption it has today.
Starting with the latest version of Angular is generally the best idea, though you may be tied to earlier versions depending on what other modules you want to use. For example, the npm version of ng-bootstrap is still tied to Angular 4 (though one can easily build one that does from the github repo). I would recommend starting with ng-cli as most (older) books will start you off with some other build system (e.g., system-js, an older webpack plugin).
If you don't know a ton of other frameworks, tools and the like AND need to get something built this quarter, learn the latest version of Angular 1.x
Otherwise, learn Angular 2, Typescript and all the other stuff that people use for building etc. all at once, focusing heavily on Typescript and core Angular concepts first.
Those horses have left the barn.