They're both tinker-tools - in the right hands, they both have their strengths.
But asking which one - that's a political question
From a developer perspective - I really do appreciate OpenWRT - it truely is open, and the team that supports that platform is supportive with documentation and open to contributions. If you're looking for a sandbox to experiment with, it's a great code baseline to work with.
DD-WRT - more consumer friendly - polished, with much functionality (some of it which I question, but that's me).