The wine should be suitably fined before this aging.
That being the case, and "all other things being equal", the main other difference between bottle and carboy aging is that in a carboy, the mass of the liquid makes it less prone to temperature change. (A consistent temp is desirable.)
While there can be desirable micro-oxygenation if you use a natural cork with bottles this is not much of a factor for only 9 months of aging.
In the end, carboys are notorious for letting in inappropriate oxygen over time one way or the other (often thru the closure). The likelihood of problems due to these issues is higher than if you bottle ... and SO, I would say make the bulk of your aging in the bottle.
The exception to the bottles, and aging in the carboy instead, is if you are very careful to use a closure method that does not allow oxygen infiltration .... and either a Better-Bottle carboy or a newer, non-banged-around, glass carboy that has not been exposed to freeze, thaw cycles (as this can cause micro-fractures in the glass). And also being able to keep the carboy at a consistent temperature.
But what it really comes down to how much of a loss will it be if the wine ends up with faults due to storage.
While it's true, you might get thru 9 months without any serious problems in just any old carboy ... the issues and practices I've mentioned above are points to consider.