Here’s the best tip I can give you when an agent or editor asks for sample chapters: Send the first chapters.
Why not send “the good chapters” of my manuscript??
Well, if you don’t send the beginning of your book, it looks like you’re hiding something.
Similarly, if you are asked to send 10 pages, send the first 10 pages – always.
Now, you may be asking, “If I have a prologue, do I send the prologue or the first 10 pages starting in Chapter 1?”
The answer is you send the pages from where the book begins — so, yeah, from your prologue if you have one.
(If this makes you nervous, then perhaps your prologue isn’t strong and you should find a way to eliminate it.)