IMO, the Forester has similar interior space as the CRV or Rav4. It's very small & tight in the front & 2nd row seating, especially with a seat in the 2nd row. Otherwise a good commuter car.
The Highlander is bigger, but still smaller than the Pilot. The main thing that turned me off from the Highlander is the 2nd row middle section, as it's not long enough to secure an infant seat base to it. The seat base would overhang too much on the Highlander 2nd row, and you would be forced to place the seat in the outward position. Also, not seat related in the rear, I'm tall so my knees touch the dash when the driver's seat is all the way back. So putting a seat directly behind the driver's seat for me wouldn't work.
In the Pilot (I'm going off of the 2009 model, since I've been looking into it a lot), there's a lot more room available in the front, 2nd, and 3rd row seating. Feels very similar to my Sequoia in terms of interior space (still bigger in the Sequoia) but there's ample amounts of room in the Pilot. If the Pilot had more power and a few other things, I'd pick one up right away. But out of the 3, that's my best choice.