Generally speaking, I find ddwrt to have more features but tomato to be more reliable. I personally like the bw graphs and ip traffic monitoring of tomato better. I can drill down with graphs and see what IP address is utilizing the most traffic real-time, in 24 hrs, weekly, etc.
Either one will honestly work. I would suggest making a backup copy of your settings, then tftp either tomato or ddwrt and try it out and see what you think. Both are better than factory default.