Obviously it depends on the project, but in general, what methodology do you prefer for developing APIs? Just simple HTTP POST / GET, XML, SOAP, REST, or? And in what format do you return the results? Raw text, name/value pairs, XML, JSON, serialized array?
I used to just pass XML request back and forth, and thought that was great. Then this young, ambitious, intelligent russian who now works for Microsoft convinced me to use SOAP for a large project we were doing together. Absolutely hated it at first, and couldn't think of a more complex way to send data between servers. Once you get the WSDL and everything in place though, it's actually great, as you don't even have to worry about the data transfer part. It's all just functions, plus it can easily be used across multiple platforms (PHP, Java, .NET, etc.).
On to REST right now, with returning either JSON or serialized arrays, depending what they want. Gotta say, I think I found a winner!
Clean, easy to develop, flexible, light-weight, and easy to learn. Perfect!
How about you other developers? What do you use for APIs, and why?