CEB's can't stand up to rain, unless they're cemented over, or if they have a good overhang. Which isn't really normal for a retaining wall, but hey you could if you like.
As for earthbags for a retaining wall, it's the same as CEB's. If you cement over, great. If you earth plaster over it, it won't work normally. If you create a great earthen plaster (after experimenting) mayyyybe you could get it to withstand the elements for a few years, depending on your climate....
Depending on the angle the bags lay, would determine what would be the best solution. If you have a straight wall, they would stand up for a long time if you don't have sideways rain often (if the bags were tamped well and cured well). I did a garden bed this way, and learned the hard way that earthen plasters don't work outside without a sufficient 'hat' and 'boots'.
Hope that helps, I can give more advice if you like!