Of the 2 image handlers, GD/IM, which is better?

[setishock]

I have GD running on my forum and it's doing fine.
But I'm just courious. Of the 2, IM or GD, which is better? Why? How do you find out if IM is available and how to activate it?

[Videx]

IM is supposed to be better, but often it's more trouble than it's worth. Some photo oriented mods may require it, but I've never seen any. Back when captcha was used it made better images, but captcha is useless now anyway.