Apple has 0 restocking fee. ATT and VZW have 10 percent. Apple has exchange to a new one, ATT and VZW to refurb during first 30 days. There are some chances to get defective one. With Apple you send it back and exchange, with Att you get refurb one.
They are the exact same thing. The only difference is that AT&T and Verizon charge a restocking fee if you return the iPhone (as in no longer want it). You can forgo the carrier after purchasing and directly deal with Apple when it comes to warranty purposes. It's just like if you bought a MBP or iPod touch from a retail store. They have their own return policies but the warranty is the same as the ones that were purchased directly from Apple.
I am ordering through Verizon because I want to transfer an upgrade. If I order from Apple I would have to bring the iPhone to a Verizon store when I get it and get them to do the transfer for me. If I order from Verizon it is less work. I also don't have to worry about my plan being changed or worrying that my first month would get my employee discount rate.
Plus your carrier will have less load on their servers relative to Apple. Usually people first go to Apple and rarely choose a carrier when purchasing a new iPhone.
One advantage with ordering from Apple is that you can buy AppleCare+ and have it enrolled automatically. Also, Apple.com will have more stock than the carriers. So chances of getting it delivered by the 21st is higher with Apple.
How about insurance? Will at&t provide me with the same insurance i currently have on my 4S if i buy the 5 from apple? I bought my 4S last year through at&t's website.