P.H.
When renting a car I order a carset. Or if the shuttle bus will be picking us up I will reserve one for that as well. I've never had to bring a car seat with us (while traveling in the US) If you can avoid bringing an awkward, hard to carry carseat, you may want to do this.
Also, I've had many strollers broken by the airlines. So now I travel w/my favorite "travel stroller" I bought at walmart for $23. It is very small, folds flat,very light weight and it reclines! It's good for up to 3yr olds, any older and their head wont fit under the canopy. I researched strollers (for travel) and this one has held up better that my $400 one.