My current WIP has a prologue that has a murder, but it doesn't involve the MC. So for me, I would have trouble deciding whether to put the prologue, which I love and I do think hooks the reader, versus the first 5 pages of chapter one, which introduces my MC and his voice a bit more and introduces the case he's working on.
Send the first five pages, exactly as requested. If that's prologue, send it. If it's not good enough to hook a reader, why is it in your manuscript?