My (borrowed) suitcase kicks ass! It's a big old Samsonite clunker from the 1950s, redwood-colored,
with brass fasteners and a lock and key! It holds mucho shit! 
It may cost as much in excess luggage fees as your fare.
It's solid but I can carry it easily, and I'm only packing clothes and toiletries. I do hope they don't charge
too much more than the $25 they quoted me on the phone. 
Here's what I found on the American Airlines website:
Overweight/Oversize Baggage Charges
Additional charges apply to this type of baggage and are collected at the airport ticket counter.
Itinerary Overweight Baggage Charges
Flights within the United States, the U.S. Virgin Islands, Puerto Rico and Canada
Checked baggage weighing over 50 lbs/23 kgs but not more than 70 lbs/32 kgs will be charged at the rate of $100 per piece.
Checked baggage weighing over 70lbs/32 kgs but not more than 100 lbs/45 kgs will be charged at the rate of $200 per piece.
Baggage weighing more than 100 lbs/45 kgs will not be accepted as checked baggage.
Oversize Baggage Charges
Checked baggage which is larger than 62 in/157 cm will be charged at the rate of $200 per piece.
Baggage measuring more than 126 in/320 cm will not be accepted as checked baggage.
So as long as your big suitcase is less than or equal to 30 inches tall, 21 inches wide and 11 inches deep, or some other combination to be less than 62 inches in length plus width plus depth, you should be fine.
If you don't have a bathroom scale but you can pick up and carry your packed suitcase yourself easily with no problems, I think that it probably weighs less than 50 pounds. If you get to the ticket counter and find that it is a little too heavy, you can take a jacket or coat or other outerwear out of your suitcase and wear or carry it and it won't count in your carry-on bag and personal item allowance.
