Recently we were asked to install a retaining wall using a concrete sleeper system with a wood grain pattern. I will be the first one to tell you that it not only looked sharp but it sure did the job. With that being said the way those systems work is the points of failure that hold the wall up are the post systems they come with, should one fail you will start to see some major erosion.
My own personal choice would be the versa-lok retaining wall system. Unlike rail ties or sleepers that rely on their own mass and posts to work, these retention wall systems all attach through their pin system, this allows the blocks a more monolithic attachment, less likely to fail and they come in many different looks and colors. Email or call us and we can come out and price them.