What firmware should I use on my router? [closed]

I've got a Linksys something or other router. I've never had any issues with the default firmware but have always wondered what I'm missing out on by not changing to a 3rd party more configurable firmware.

What should I consider changing to? What does I gain by switching to it?

Another alternative: DD-WRT:

DD-WRT is a Linux based alternative OpenSource firmware suitable for a great variety of WLAN routers and embedded systems. The main emphasis lies on providing the easiest possible handling while at the same time supporting a great number of functionalities within the framework of the respective hardware platform used.

You can try OpenWRT. It supports a broad range of hardware and has many packages in a repo. It feels like a solid Linux system. There is also a good web configuration interface available.

I'm using it and think that it is very nice.