OP - I have had horrible experiences getting AZ to put me in their "extra legroom" or whatever they call it seats. Their call center in Albania is awful and most agents rude. Whatever you do, try to avoid AZ ticket stock at least.
AZ will assign the seats to you at the airport for free, if any are left. I called maybe 10 times to get seats ahead of time and was shot down every time. Those super kind agents also left notes every time, so the Supervisor at check in at JFK thought it funny to mention the notes they left. Ugh. Got 3 of 4 extra legroom seats for my party; 1 person sat in a normal seat.
AF and KLM are happy to assign seats ahead of time. Service is similar to AZ. Greater chance of free upgrade on AF (to W). And forget about any sort of DoD upgrades on AZ - they asked for 1800 EUR per seat at the gate for a lie flat seat when I was on a V fare.