Airline fare question. I'm booking my first flight. I will be traveling alone. What're the differences between main cabin and basic Econ?

My saved bookings go through either AA ord Delta. I'm trying to figure out the differences between the main cabin and basic Econ. I'm willing to pay the extra 60-70 bucks if it's truely worth it. I'm not worried about earning miles or cancellations and changes. I know the selling point is seat selection, but how does that work? Do you pay for the higher fare like a premium but still have to pay for the selected seat? Is there extra leg room? Are amenities like Wi-Fi, movies, drinks affected?

Main Cabin is nicer and you get more room, better service, and less stressful over all. Basic is just a lumpy seat and nothing else.

It's nicer. I would pay more depending on the length of the flight. I can sit anywhere for under 3 hours, but more than 3, and I'll pay for upgraded seating.

Each airline gives their own names to fares and offers different services for each.
AA Basic Economy - Seats assigned at check-in, Not eligible for upgrades, No flight changes or refunds, Board in last group
AA Main Cabin - Choose your seat (fee may apply), Eligible for upgrades on American flights, Flight changes allowed (fee applies), General boarding

Customers flying Basic Economy are now allowed 1 free carry-on (in addition to a personal item) to all destinations. You must review checked bag fees if checking a bag.

For American Airlines, Main Cabin appears that the difference is only getting a seat assigned at ticketing, and less likely to be out of space in the overhead. Flights are not changeable or refundable at all in basic economy.
Neither fare includes any more than a soft drink and basic entertainment. Wi-Fi not included.

Delta basic says No advance seat assignment and seems similar to AA in the features.
Both may give you a tiny bag of pretzels or nuts for free.

Looks like the difference is when you get a seat assignment (at ticketing vs check-in), ability to buy upgrade seats, time of boarding, ability to change the ticket at a fee.

Extra legroom seats are a fee on top of the Main Cabin cost difference.
Wi-Fi I believe is typically at a fee for both
Soft drink and very tiny snack included on both
One carry-on included on both

In Economy, since last to board, your carry-on may end up as checked baggage at no fee at the gate because overhead storage fills and economy is last to board.
In economy, most likely end up with a middle seat towards the back on most flights.
Seat is assigned when you check-in within 24 hours of the flight.
You are also more likely to get bumped in overbooking and compensated for that bump, though it isn't common if you check-in at home 12 to 20 hours ahead of the flight.

CHEAPER PRICE has less extras.

Seat size the same. You do not pick your seat. Any changes either not allowed or expensive.

NO REFUND means exactly what it says.
depends on the flight Airline on the extras.
You decide do you just want to get there as cheap as possible or do you want the extras.

Suggest using seat guru and explore what they say about the plane for your desired flight.

The grounding of planes has cut tens of thousands of seats out of capacity.Expect summer travel planes to be full or near full for almost all flights.

Delta
With Some Key Differences

In Basic Economy you'll experience:

Complimentary carry-on bag. Overhead bin space may be limited, so your carry-on bag may be gate checked free of charge
Checked bag fee applies depending on the route. Please visit our Baggage and Travel Fees page for details
Seat assigned after check-in
Ticket changes or upgrades are not allowed*

* Ticket changes or refunds not allowed after the Risk-Free Cancellation period. Basic Economy travelers are not eligible for paid or complimentary access or upgrades to premium seats, including to Delta Comfort+® or Preferred Seats; and no paid access to Priority Boarding.

You can expect a middle seat as the window and aisle seats will be the premium ones.

It is the same cabin just a different fare for the seat you occupy.

Deltas Main Cabin Extra are specific seats in the main cabin that have slightly more leg room