Single-mode would be attractive from the point of view that it could be used for everything, so you don't need an annoying and unwieldy mix of single-and multimode.
On the other hand, you will need to buy singlemode transceivers which are much more expensive than multimode ones. If you have a hundred 10Gb links to put in, that cost difference would be serious: looking at the last prices I've had, 100 10Gb MM would be $13K, whereas SM would cost $52K.