Mountaneer is an addon that aims to make mounting easier when you have a large collection of them. It provides slashcommands to mount. You can choose to mount by category (eg. a random land mount, random flying mount), by speed (slow, fast, extremely fast), by (partial) name, or any combination thereof.
So now you can choose to just mount a "random epic flying mount" which will always work with all the mounts you have, without having to edit anything. Mounting "the best I can" in specific places (eg. a fast land mount in dalaran) is also planned, but not yet implemented.
use "/mount help" if you need help.
Basic usage involves:
/mount land fast random - for a random fast land mount
/mount flying fast gryphon - for a random fast flying gryphon
/mount max - for a the fastest random mount possible in that location. This is dalaran aware, so it will mount an epic land mount in the city, and a flying when on the landing.
More info can be found on the Chat commands wiki page