Generally there are 3 types of retaining wall used in Landscaping, which type is determined by budget and what type of ground is to be retained. If you consider the options below you will identify your type of wall both in appearance and suitability:
Where you have new ground or ground that is likely to move a flat laid 6 inch thick concrete block would be the most suitable as it's heavy and strong. If the face of the wall is hidden then there is no need to do anything with the surface. This would be the most cost effective wall, however if the face was visible some form of facing would be required as it is not particularly attractive in the landscaping context. Facing of this type of wall could be, exterior masonry paint, render or facing brick. Using facing bricks is the most costly approach however it does provide the best long lasting finish.