I have done it both ways... two seats in Business and using a bassinet and three seats in economy. Honestly, it's a wash.

Even though our daughter was well behaved on almost every flight, Business class is a bit stressful if she's awake. You get tired quickly of holding her and she doesn't always want to stay in the bassinet. We found ourselves often a bit stressed, worrying about bother other pax, etc., and didn't often fully enjoy Biz service.

In economy, we booked 3 seats together and were able to use the car seat in the middle seat. This worked like a charm on several A330 flights... the last four rows of economy are 2-3-2 instead of 2-4-2. This was great... a row to ourselves, the bathrooms and galley close by, and the FAs seemed more inclined to help us back there.

Also, in the car seat, our baby was much more likely to sleep. Once she was asleep from takeoff to touchdown AMS-MSP. She also did very well on several DL MAN-ATL flights on 767s (2-3-2) and some flights from EU-south America on 777s (again, 3 seats in the middle).

She also earned miles and became a gold elite before her first birthday!

Of course, the best solution was for us all to fly in J... a couple of times we've purchased 3 seats in biz. The problem here is that, unless you're on a 2-3-2 777 or a 747 main deck, you're not all sitting together.

Hope this helps.