I like both actually but I feel more comfortable using the cute little trailer that the kids can ride in. I like it because its safer, if you accidently fell off your bike or crashed it would affect the child in the child seat, but if you used the trailer, it would probably just bump around. The child is much better hurting him/herself in the trailer than hitting concrete or gravel.
You can fall on a bike and the trailer will stay upright. A trailer will be more comfortable, carry more things and have screens for bugs when you stop.