Paypal Websites Payment standard IPN VS Paypal Express Checkout

I have Paypal Websites Payment standard IPN installed on my server, and that is what I have been using for the last 5 years.

Can someone tell me the difference between using this module and using the Paypal Express Checkout

All of the differences, I cannot find anywhere to read about this.

The reason I am asking is because Paypal has a credit card processing that is cheaper then my authorize.net, but I must also use the Paypal Express Checkout to get the rate.

I know in the past there was a reason why I didnt use the express checkout but I can't remember why, I would like a list of the similarities and differences between the 2 if possible. And how the flow works. my site is mysticcrypt.com you can see how it functions now in the checkout process.

Start here:

http://www.zen-cart.com/content.php?70-whats-the-difference-between-paypal-standard-express-and-pro

There used to be differences between IPN and Express (I think at one time you needed a Paypal account to pay through Express, which might be the limitation you were thinking of), but your customer sees the same thing now and Express is much more reliable than IPN.