We had a Hamax, and it was very good. Still got it actually, although Little Cudzo is too tall for it now. There are various models, ours was called Smile
but they only really differ in that some have a mechanism which can tilt the seat backwards. This is only of real use with very small children who are likely to fall asleep in the seat. The "frame" which attaches to the down tube is nice and rigid, so it doesn't sway too much, and because it fits to the frame you can still carry panniers (or use it without a rack) but there isn't going to be room for a saddle bag or rack pack.
Whatever you choose, you'll need mudguards - splashing through puddles was great fun for our son. It's also good hill-climb training, as your child is likely to push you in the back up hill to show their displeasure at the lack of speed!