let's link to this page and keep it up-to-date, rather then the 200 wiki-pages for each device! To avoid confusion this needs to be as straight forward as possible.

You decided to simply download a firmware offered here. Good. Luckily even here we have a variety to select from. Do you want to use a firmware based on stable sources or one based on bleeding edge sources? We recommend stable. To satisfy your curiosity your can read about the different branches here history.

Although the trunk images offered for download are usually pretty stable, OpenWrt is not a rolling release. There is always a stable version. It is of course possible that your device or the hardware version of your device, is not supported in the latest stable. There will be no backports, you have to use bleeding edge in that case.

 http://downloads.openwrt.org/attitude_adjustment/ 

 http://downloads.openwrt.org/attitude_adjustment/12.09-rc2/ 

NOTE: 12.09-rc2 is considered final version unless something serious come up.

Files precompiled from the bleeding edge code branch, are always here:

 http://downloads.openwrt.org/snapshots/trunk/  

If there are different image files for different hardware versions, you must use one for your hardware version. Do not neglect this! E.g. see dir-615, different letter can mean completely different hardware!. It is also possible, that a newer hardware version is only supported in the bleeding edge sources or not yet supported at all. If your version is not explicitly marked as supported you should ask in the forum. Then come back and update the wiki!

Sometimes there is a image file with the word factory in the name. If there is one, you must flash this one over an OEM (factory) firmware.

Sometimes (depends on the maintainer) two different versions are offered for download: JFFS2 and SquashFS. We recommend SquashFS-Images.

Please read header to understand the differences. It doesn't hurt to read flash.layout as well.

Usually an imagefile with the word "sysupgrade" is offered as well. This is for sysupgrading OpenWrt only!