They're all so close quality wise.
A'bunadh and Macallan CS are basically the same profile. You may find yourself wanting one more than the other, but they're good substitutes for each other.
Glenfarclas 105 is a totally different beast. The other two are lovely dessert drams, while this one is more of a nightcap--lots of complexity, a little smokey cocoa maybe?
Anyway, they're all great. Buy ((A'bunadh or Macallan CS) and Glenfarclas 105).