Hi. What is the best image file format to use for textures? Thanks.
-Laurifer
As far as I know it should be the best format
for regular pictures files, therefore the best format
fot textures would be .jpg
When saving a file as JPG, it’s often compressed, resulting in data and quality loss. This happens everytime you save it, if you don’t tell the program not to compress it. I’d use Targas. They are a lot bigger, but no data is lost when saving them, and they support alpha channels.
Yes! Use Targa! As egg says, Targa is bigger. I heard .jpg compression gets rid of details the eye can hardly see! 
So, you are definitely better off with Targa.
JPG has lossy compression, you should always avoid it unless for web publication.
PNG has non-lossy compression, it is very good for everything
TGA TIFF etc are more or less equal but their compression algorithm is not as good as PNG AFAIK
raw TGA etc has no compression at all… not a smart thing to use.
Stefano
Depends on what kind of texture.
If the texture is from a noisy source, such as tree bark, grass, etc., I prefer JPG. Otherwise PNG.
for color: any of the supported formats
for transparency: any format that supports black-white 
for combined: TGA, PNG (if you want to embed the alpha channel)
Thank you all!
-Laurifer