Get one that's well padded and well ventilated. Then make your baby get used to it. No baby likes being strapped down compared to being carried. Safety vs babys preference.

This is always essential reading to me: http://thecarseatlady.com/keeping-your-kids-happy/

If your child has been used to being carried during the car ride, usually they will protest when first trying to get them in the car seat.
Otherwise depends on age, check on the adjustment or recline of the car seat.

From experience, getting the child to use a car seat is getting them into the habit.
Maybe try distracting them while they're in the car seat at first or while you're trying to put them in.

Hopefully this helps you out.