Hi. This is my first post. I am currently in the process of booking myself and my family for trip to mexico. Within the expedia checkout process I am asked for the frequent-flyer credentials for each person and this got me thinking, I should enroll in a frequent-flyers program. I've heard of people getting free flights, and upgrades but I'm skeptical as to if the hype is true or not. I guess my question is this:

What frequent-flyer program should I enroll in? Its an AA flight. Briefly, how does this system work? Can I redeem the miles flown by the rest of my family members? Is enrolling in frequent flyer worth it? Because it seems like a lot of footwork/overhead just to get upgrades?

Thank you.