I'd ask what are your budget considerations and how you intend to use it. Assuming it will become part of your normal transportation and costs are secondary, the up-front Bobike is a blast. While kids quickly out-grow it, as they say, "they are only young once."
If you want something you can get a little more mileage from, the rear-mount Bobike can carry kids pretty much as long as they'll need carried. Both are rock solid and will last through the entirety of your fecund years. ;-) Also, both swap easily among bikes if you buy a second rack.
In any case, I'd suggest giving the guys at
Clever Cycles a call. They sell more kid seats in a season than most shops sell ever. And they ship. If he's around Todd would probably be the best person to ask to speak with. Of course, this assumes you intend to buy from them. As our good friend Mr. Thill has commented, nothing worse than chatting up a sole-proprietor then taking your business to the internets. ;-)
As for the Copilots, I have one.I got it before the Dutch invasion as it were. Not a waste of money, but more of a weekend/recreational item than something built for daily transportation.
Best of luck,
-Allan