As I mentioned in my post my two main reasons were because I have credit vouchers for Delta and because Delta will allow me to choose seats beforehand rather than worry when we check in that we won't be able to get 5 seats together.
It's just like when any product goes on sale and causes price competition...am I going to choose the one that did it first to "reward" them or am I going to choose the best product for my family? In this case Delta is the best choice for us.
Although it's a moot point for us anyway because dh nixed the trip