Those are all great series, but as far as where someone should start? Depends on how familiar they are with this stuff. Have they seen the movies or cartoons and have a general idea of the character interactions such as the relationship between jean and scott and Logan? I'd go with Astonishing and move on to things like House of M so on and so forth up to the present.
If not.....I dunno. I'd probably still start with Astonishing as it establishes the characters in an amazing way. I've gone back and read some of the older stuff like Dark Phoenix saga and honestly I don't think a modern fan who isn't accustomed to comics would be able to relate to the writing style of it. God Loves man Kills? Beautiful work, a little hard to grasp without understanding the characters, but it's like a classic lit novel that stands the test of time. You don't need to start with it, but it is something to read when you want to read something and be moved.
I'm pretty new to comics, but X-men is my focus. Love the characters, the lore, the dynamics between characters, and how the X-Men are considered completely different from other superhumans.