Depend on your budget actually..

For me, i buy separately stroller and car seat, and again depend on your budget!!

I've experience using the cheap one and on unfortunately day when driving the car during the heavy rain, the car skid threw the off road and the baby were upside down in the car. After that i throw away the cheap one (RM1++.++) because there's no secure belt and buy the expensive one (RM5++.++) which have 4 point harness and have additional secure belt to reinforce the oem car seat belt.

From my view, the more expensive, the more safe for your baby because they have a good engineering method to secure your baby.