What are the advantages/disadvantages of a PhD advisor who is experienced vs. one at the beginning of his career?
It is sometimes assumed that less experienced / competent supervisor will try harder instead, spending more working time and will be somewhat a friend to you, not just a teacher. However this depends. A younger supervisor may also choose to give you only the minimum required amount of time.

For a good PhD student, it may be most important to get a good project and ideas that, as a rule, work. This does not require lots of time but does require a lot of competence. I would normally select the more experienced supervisor even if one may have less time for me. Only if the studies require some complex, difficult to learn methods, a younger supervisor who still uses these methods directly and personally at work may teach them more efficiently.