First, only cuda-10 is officially supported by nvidia in ubuntu 18.
Second, this new image fills the gap in having a dual cuda image ready to load on your disk, the previous ubuntu 16 image included cuda-8 only.
Third, more than a thing is not working at its best in ubuntu 18, there are some problems, more or less significant with curl, tempcontrol and compilation in general because of the updated gcc suite.
In short, as long as you run miners designed for cuda 8/9 I recommend to go with ubuntu 16. Te other images are still valid, it's all up to your preferences or experiences.