Semantics

As the author of seven books of non fiction and three YA novels, I am wondering what would be the best way of presenting my new novel:
1) This is my fourth novel
2) This is my fourth novel, first for adults
3) This is my first novel
4) This is my first novel for adults

5) Does it really matter one way or the other? Assuming everything else being equal (ie. that the novel is any good) I've heard that sometimes a first novel is easier to sell than a fourth novel (especially if the other three novels haven't achieved Grisham sales levels). In that case, maybe I'd be better off with a pen name for the new novel (even though all the YA novels are now out of print).

I'm still wondering, as far as novels go, which is more commercial, to be considered a first novelist or someone on his fourth novel, and how much does the YA/Adult distinction make a difference to an aquiring editor.

To be a little more specific, the fiction was with Houghton Mifflin, the non-fiction with Macmillan, Holt, Scholastic, Schirmer and Harper Collins. As far as sales figures, who can follow royalty statements? Let's just say, it was nothing astronomical.
If I'm reading you correctly, you're saying I should bill this as my fourth novel and leave it at that?

My feeling was, especially in approaching a new agent with a manuscript, that they might be more impressed if they knew I've published fiction before.
But then, on the other hand, I was worried that if I've already published three novels, they might consider me terminally mid-list.