I have always preferred PNG format, not only because it is small, but also it is Open Source! Gotta love that!
The PNG image file format is now more popular than GIF
“Summary:
The PNG image file format has been created in 1995 as a response to some patent issues around the then-prevailing GIF format. PNG has gained popularity ever since, and it is now used on more websites than GIF.
PNG is now used on 62.4% of all websites, just ahead of GIF with 62.3%. GIF was leading by more than 15% one year ago.
PNG is now the most popular lossless image compression format on the web. Only the lossy JPEG, which is the most appropriate format for photographs, is used on more sites.
While GIF’s patent issues mentioned above are long resolved, it’s the technical superiority that now convinces webmasters to chose PNG over GIF. PNG results in smaller files most of the time, it supports a much wider range of color depths and transparency options. The only feature where GIF still shines is its support for animation. However, most people find that dancing icons on a website make it look like it hasn’t been redesigned in the last 15 years. Animation is mostly used for ads nowadays, and even there, animated GIF’s would be considered the poor mans alternative to Flash.
Interestingly, GIF is still more popular than PNG on the top 1,000 websites (67.9% vs. 66.3%, see our head-to-head comparison), but we can expect that to change also within the next months. The trend is very clear: for every site that changes from PNG to GIF, more than 3 sites make the change in the other direction, see our technology change report.
There are some remarkable geographical differences in the usage rate of PNG: it is very popular in Europe, with over 70% in France, Italy, Spain and Netherlands, but much less in Asia, with 41% in Japan, 34.6% in Korea and only 30.6% in China. Usage is also higher on Unix-like systems than on Windows, and Google seems to be a big PNG supporter, it is used on 95.6% of all Google Servers.
The GIF image format, originally developed by CompuServe more than 25 years ago, was a very important standard in the early days of the web. It will probably be around for another 25 years, but it has been dethroned today.”