Depending on the airline, LX, AF, LH are the ones that block those seats exclusively for parents with infant. E.g. We couldn't get a row bulkhead all my ourselves for our LH flight, since we had 1 infant, we can max. get 2 seats on the bassinet row.

Of course they are based on first come first serve basis, which means that they could be completely booked up when you book your flight.

As much as we all love travelling in J, for a 4 hour flight I'd opt for 3Y. I've done both and for a longhaul, baby and I'd be both more comfortable in J even with taking turns holding a sleeping/fully awake id and eating in shifts.

But for a shorter flight I'd give up a bit of comfort so that we could lie the sleeping child down across the third seat or he/she can sit up and watch the IFE, read the inflight magazine or Skymall ;). Regardless if the seat is in Y or J, I expect to have to likely eat in shift and hold a sleepy child for a certain period of time.

As for priority access, I have found that travelling with a small child (works well when you're with a stroller) especially in Europe and more and more in North American, I get called over to priority line for customs & immigrations and security screening. I always check-in on line and only need to stand in line for baggage drop off.

It really depends on the airline and/or route flown.

We flew 4 hours from Singapore to Taipei, it was okay in Y.

We flew 18 hours from Los Angeles to Singapore, and I wouldn't go anything less than J.

I wrote about it http://www.connectcto.com/w/2011/08/...with-toddlers/

+1^

always, always get the baby a seat. it will make your life better. If you can't afford 3 in J, do 3 in Y.