Obviously it's subjective.
I love the bat mount, but I think the Iron Skyreaver is ugly. The feydragon is amazing but I think the Winged Guardian and Heart of the Aspect are kinda meh. I actually kinda like the weirdo goofy goat mount that everyone else seems to hate along with the sparklepony, but not more than average. I like the CM Phoenixes quite a bit, and would probably choose them over every store mount except the bat and the feydragon.
It would be nice if they had in-game variations of the super unique ones like the bat and feydraon, but I don't feel like the store gets all the good mounts while the "free" ones suck. There are tons of mounts available to earn that I really really like, many of them moreso than the purchased ones.
But that's just me.