I would agree with Darren, although I mainly use JPG's just because of the file size compression.

It really depends what the image is going to be used for, does it have to be small, good quality, transparent, animated?

Genrally, I use jpegs, pretty good quality and decently sized files. If it's animated, I use a GIF, if it needs to be transparent I use a PNG and so on.

-Kanuck

jpg has the best compression, followed by png and finally gif's. at least that is how i think it goes. it also depends on what your trying to do to as Kanuck said

I would have to say for web i use .jpg due to its small file size.

for editing .psd *photoshop document*

Tiff i use allot at my workplace. its good for big images with exelent quality.

bmp is good for screenshots for you to keep on you pc, but the size is large compared to the jpg

gif i use ocasionaly.

Tip: if you have adobe photoshop or macromedia fireworks. do a save for web, or a publish. mess around with the settings and see what one looks best and has the lowest file size.

Remember that things like .psd most people can not view! so put it in a gif, bmp, jpg or similar for e-mails, web, and transfering to a computer that may not have a graphics edetor.

Keep in mind thought that JPG is not lossless, it is a lossy compression. You should never be saving master copies of any work in JPG format for just this reason.

PNG (pronounced "ping") and GIF on the other hand are lossless, which is why, pixel for pixel they can never yield the kind of compression that JPG can. GIF has always had patent issues from Unisys. Most of these patents are now expiring but GIF was (and still is) frowned upon by most OSS web developers, including myself. Because of this, I choose PNG for nearly all of my images that I can. JPG comes in second and is only used when I care about really reducing the filesize.

-Weaver