R.D.
We have Britax Roundabouts, which I selected based on the Consumer Reports data of safety ratings and ease of install. We have one in each car, but will transfer for travel (plane, rental car) or another family member every so often. I've never had a problem installing it anywhere -- it goes in quick and tight. My mom bought a Cosco seat for her car since she lives in the same town as us and watches him more frequently and that thing is a pain to install and I never feel comfortable that it's in as tightly as it could be. She has the same model car as my SIL, so I know it's the carseat and not her car.