If you want to compare vehicles...I highly recommend this site.
According to this and from all of my own recent car buying research, the Honda is going to give you a little more space with the third row collapsed. It also has a tiny bit more space with the third row up. Having been in both, I felt the Pilot was less cramped. The Pilot has lower expected reliability (read about a number of transmission issues), but the Highlander also doesn't rank as high as other Toyota models either. Although, reliability is a complicated formula that often unfairly includes brand reliability and previous model version reliability that has no bearings on the current vehicle in question.
If you're looking at the Mazda as well, it was my fave of those three. It was a bit too small for us and I hate that it lacks a touch screen, but it's a fun ride and the model I tested had an awesome red interior.