I have found out with NWA when making an online reservation, that you can go on line 90 days out and pick your own seats also. Just go to reservations and click on your itinerary and then scroll down until you see - choose your seats for this flight. They have elite seats with star that are available but if you are not an elite traveler the system comes back and says your seat will be assigned at check in. You can choose any other available seat but they do block the exit rows as if they were all ready chosen. 90 days out NWA will pick seats for you, and if you're unlucky like me they give you the very last row. But I changed that. Rather be up front but will try for that on check in.
You would need to pick your return seats later than your outgoing seats as they can't be picked until 90 days out either.