Best way to take baby on bike ride . . .

[Jolt]

I would think the car seat in the trailer is the safer way to go (much less risk to him if, God forbid, you were to crash), although it would be a much bumpier ride than having him in the Bjorn. Maybe the trailers should be made with some sort of suspension to smooth out the bumps. If there's a way to configure the car seat so he's just about lying flat, that should make the fact that he can't yet hold his head up a non-issue (but still cushion his head and place padding around it to keep it securely in place).

ETA: What do people with babies/small kids do in countries where cycling is a routine form of transport and many people don't have cars? They must have ways of taking the kids along when they do their errands etc.--I don't suppose they just stay home. Seems that those would be the places to look for safe and practical solutions here.