I thought my Shadow Priest was the most boring character I leveled - next to my Druid (who I wanted to love, but didn't).
As for these Heirlooms - what are they? I never got to that point, and I don't quite get it. How do you buy them, exactly? And from what I understand, you can use them on any character you want (I assume you mail them - and they bind to your account)?
An heirloom is an old level 60 item on steroids.
See, they took ordinary high-end items from back when the level cap was 60, and turned them into leveled monsters. They follow your level, and increase in power along with you. They are also very good for whatever level you are at. If you give it to one of your characters that's level 1, it'll be adapted to level 1, the stats getting better and better as your progress.
In addition to that, they also give you more experience when using them on a character.
They are indeed bound to your account, so you can mail it to one character, use it, then mail it to another.
You buy them from an Heirloom Vendor in Dalaran, in exchange for a certain type of emblem.