Isn't Tomato way out of date? Wikipedia shows the last stable release was almost 5 years ago, and the website shows no dates on its releases (not a good sign). I ran Tomato for a long time and loved it, but I just got too nervous running such old software as the gateway to my network. Ended up upgrading to a cheap TP-Link router, switching to the latest and greatest OpenWRT release, and haven't had any complaints at all.

OpenWRT tracks upstream software as well as the desktop Linux distros do, and it's what the upstream developers use. DD-WRT and Tomato put their own web interface on things but often leave important parts of the system out of date for very long times, especially when they're being held back by proprietary drivers. If you want to make full use of the features and stability and security of modern Linux networking, OpenWRT is where to start: you know you're getting proper IPv6 support, state of the art QoS stuff many DD-WRT and Tomato devs haven't even heard of let alone understand, and a current kernel.

You can disable their http/https/telnet interfaces and stick to ssh with key auth for administrative tasks. That alone should help.

Also, they come with upnp and other unnecessary daemons disabled which greatly reduces their attack surface.