Opinions on Alternatives to Cisco Routers?

An anonymous reader asks: "I'm currently working on a project that is 'partnered' with Cisco. Despite that they make good routers, the company's relatively large size does not appear to be willing to meeting unique, customized, requirements. So what are your opinions of the alternatives: 3com, Juniper, etc? Anyone had bad/good experience with these companies? Are all their routers really essentially the same? How about comparative performance with totally customized routing solutions via Linux+Zebra or some other open solution?"