Well, jpg files are preferred if your banner is a picture. Gif is the smallest available format, but it is limited in color. It can only have 256 different colors (picked out of the 16 million defined byt the 256 tones of blue, red and green), so it is ideal for computer made logos or text with few gradients, or a limited color palette. Png offers the best of both jpg and gif quality, at the expense of space : they'll take more mB for the same quality of a jpg or gif, but won't have any of their limitations.
So if you're unsure, make a png and convert it to both jpg and gif, zoom it way up to see the fine parts, and pick the one that looks best.
ok so no more jpg files then, thanks for explaining that to me.
Well, jpg files are preferred if your banner is a picture. Gif is the smallest available format, but it is limited in color. It can only have 256 different colors (picked out of the 16 million defined byt the 256 tones of blue, red and green), so it is ideal for computer made logos or text with few gradients, or a limited color palette. Png offers the best of both jpg and gif quality, at the expense of space : they'll take more mB for the same quality of a jpg or gif, but won't have any of their limitations.
So if you're unsure, make a png and convert it to both jpg and gif, zoom it way up to see the fine parts, and pick the one that looks best.