We also did not want to trust a rented car seat for a few reasons (no information about accident history is one, quality generally or possibility of an outdated or less safe model than we have is another, plus we are comfortable installing the one we have). Our older son was 5 on our last trip. We had purchased a travel cover for his car seat and brought it. We checked it on the plane.
For stroller rental, we needed a double and had a great experience with Kingdom Strollers for a 15 day rental. We got a great rate compared to other companies, when we had questions before and after the trip, they were highly responsive, they were able to drop the stroller at a universal hotel and pick it up at Disney and were generally pleasant to work with. We did not have to be present for pick up or drop off. They even threw in a cooler bag (which we used constantly) and rain cover (also used), and we purchased insurance. The stroller was a city mini double - we have a city mini at home and like the way they handle. I believe they also carry bob strollers. It was in great condition. We would definitely use them again and I can recommend them without reservation.
Good luck!