These three axioms are all equivalent*, meaning that, once you assume the first two traditional axioms of a Hilbert system (i.e., $p\to(q\to p)$ and $(p\to(q\to r))\to((p\to q)\to(p\to r))$), assuming any one of the three axioms you list will allow you to prove both of the others (such proofs are left as an exercise to the reader). The only reasons to prefer one formulation over another are (a) a specific formulation might yield shorter/easier proofs that you care about in the early stages of deriving propositional calculus, and (b) the text you're using might make use of a specific version.
Also note that there really is no single Hilbert system; the term refers to a type of system, of which there are numerous instances, each with its own set of axioms. However, each system is capable of proving the exact same propositions, albeit in different ways (at least, once you segregate the systems into classical logic, intuitionistic logic, etc., the latter class proving only a proper subset of the statements proven by the former).
* For the sake of full disclosure, I'm only certain that (2) and (3) are equivalent; I've never seen (1) before, but its similarity to (3) is enough for now to convince me that it's equivalent to the others.