Actually both works fine for my router, but I prefer using dd-wrt more.
For OpenWrt, the firewall seems having some funny issue with NOW TV modem, need reset one or two times to function correctly, now I am using it. But the latest version Kamikaze doesn't work with my router anymore, looks like the flashing is failed, nothing changed but just cannot boot after flashing to Kamikaze, have to rollback to White Russian to make it work.
For dd-wrt, there is no such problem, but the latest version, v24 beta, doesn't work with my wireless, only v23 SP3 does, strange but seems a common problem as shown in mailing list.