Integrating payment solutions from 3rd parties?

[Webwork]

I'm looking into PayPal and Authorize.net as payment systems for 2 ventures. The most important will involve people paying for ad listings at various sites, with central billing. The second is straight ecom which will involve selling handmade products made by artisans. I will be handling online marketing for multiple artisans.

I'd appreciate people sharing their latest experience with either PayPal or Authorize.net. My questions relate mostly to:

1) Ease of integration; (I'm admin of Win2K server)
2) Support by A.net or PP;
3) Customer issues using either;
4) Cost effectiveness of either;
5) Is there currently a better system;

I know issues like these are raised time and again. I've read many posts. What I see is that issues about any payment system change from time to time and that's why I'm asking right now - because I'm about to make a move.

Thanks for your input.

[raywood]

I've not worked with Authorize.net. I did many third party payment processors in standard ASP. They were quite easy to implement.
I just finished two weeks ago a paypal integration in ASP.NET for a client. The paypal documentation is clear and easy to understand. The implementation was easy to do.
There have been no problems that I know of with customer usability. The client's website is doing brisk business, so I assume that the payment process is user friendly for his customer base. My client seems to think the cost is reasonable.