B757 and A319 in first
 

What are the differences between these planes in first class? Seats, IFE, comfort, quietness, etc? Thanks

I've noticed no substantial difference in first between the A320 and the B757. Coach, now that's another matter. Always fly the A320 if you have a choice and have to sit in the back.

If you had a 4 1/2 hour flight in either a A319 or 757 which would you pick and why?

I'd probably opt for the 757. Bigger plane=bigger wing = smoother ride. The 319 cabin is slightly wider, but not a big difference in first. The differences in total are not substantial, but given a choice I'd go for the boeing.

For NW, the 319 is quite newer.

Having just recently returned from a mileage run to MCO from YEG, I travelled on lots of different metal. I really liked the economy seats directly behind first on the A319, which I believe is row 5. It offers lots of legroom.

The bulkhead seats, especially in coach, are generally much better, IMHO, more leg room and arm rest trays (which can be used folded in half) and window and center pax can get out without requiring anyone to move.