Help me find the best open source router

You don't really specify what type of router you are looking for but if you are talking about a gateway router I recommend PFSense. This software solutions can be installed on youf own hardware or you can purchase an appliance to run it on. PFSense can scale from home use to enterprise use if you select the proper hardware. Netgate is the business side of PFSense and offers the software for free. Netgate sells appliances and support for PFSense if you need it. There is a bit of a learning curve but that is true of any solution.