I went to the link you posted to learn more about GIF's. I am the person who came up with graphic at the top pf the page. I am self taught in the graphics area and you seem to be knowledgeable. I needed a transparent background so automatically went to a png file. I have the ability to save as a gif in photoshop but I guess I thought that it wouldn't be a very high quality. Could you tell me more about why a Gif would be better?
This is a good explanation: http://www.sitepoint.com/blogs/2009/08/03/gif-png-jpg-which-one-to-use/
In general you are very right about what you say (as far as I know). GIF is lower quality and lower size. It is usually the choice for graphics such as banners because the quality is good enough and it is faster to download and display. But for photos JPG is the best choice. GIF doesn't display all the colors and photos in GIF will usually look deffective.
PNG is the best quality among the small-sized types, but it is also bigger in size and weight as you well say. However, as you well say too, PNG supports transparencies and the others don't.
So usually what happens is that transparencies and PNGs are not used for banners or logos or anything in web pages because usually you can get the same quality with lower weight in GIF and JPG, and trasnparencies are not usually necessary.
For instance I don't know why this site uses a transparent PNG for the title. I believe that Cort thinks that Google will find it by the written title and that is why you are doing that solution of using a semi-transparent PNG over the HTML text of the title. I can't tell for sure that I am right about this but I think it is a mistake, and that Google won't find the forum for the title text but for the internal HTML code of each page. Therefore, unless I am wrong (could be) I think that just a GIF banner of logo & text is the normal practice for a better designed banner & text.
- GIF --> graphics of any kind
- JPG --> photos
- PNG --> when you want the best quality and/or transparencies above loading speed.
One more reason to consider is that web sites owners pay for their hosting according to the traffic of MB or GB per month they have. If they have heavy images in their site they will have more traffic of GB at the end of the month, meaning paying more for more data transmission. So, both the owner and the visitor benefit from light weight images in each page.
But anyway, don't take what I say for 100% sure. I can be outdated.