On the midwife experience - with my first, I saw on ob for 6 months, then after moving switched to a group of midwives who are part of an ob practice. They gave MUCH more face time, and I love how much they tried to educate and empower me to take birthing classes (I used hypnobirthing and no pain meds during delivery), tour the hospital, make a birth plan, make a post-birth plan. They are known in the hospital, so the nurses knew to follow their lead and not ask about drugs or pain levels at all. They urged me to use the hospital bathtub (which I practically ran to), and didn't keep me hooked up to monitors (under my consent of course) and just intermittently checked the baby (who was fine). With one midwife on call at a time, she had 3 other deliveries with mine (I was her last), and so she was there almost constantly the last 2-3 hours (before that I really didn't need her).
What I loved about the practice, was that I was able to meet a couple of the ob's. This was important to me, because in the off chance I needed a c-section I didn't want to have a complete stranger or really no background in the process.
I had seen my former OB for over 10 years, and while it was difficult to leave, I am SO relieved that I did. She was very busy with a LOT of patients, and our visits didn't really inform me about much of anything.
As for the "how do you know" question... I'm a little more empirical about it. I don't think intuition is always accurate, but I trust the physical symptoms that I experience a lot. I had spotting with my first, but also increasing nausea and fatigue. I felt like I was getting "more pregnant," not less (and was very worried about miscarrying due to family history). In the end there isn't much you can do, but patiently wait. That anxiety is a set up for the rest of your life, where you will undoubtedly spend every moment trying to protect this little one. It's adaptive and yet impossible to do.