There are different strategies for playing World of Warcraft - some choose to try as many characters as possible, and some stick to one.
I've tried both. When you choose to play one character, you dedicate all your time to it and you can fully develop it, including reputation among all factions. You can't imagine that all your characters will be Exalted from Ogri'La, for example - that's just a road to nowhere. With one char it is possible.
For almost a year and a half I developed my one and only character - Gnome Frost Mage "Micromantica". She excelled at driving Frostbolts all the way to Garrosh, went solo on a few old raids, is a Loremaster and Explorer (because I like maps and I like quests to tell me more WoW stories!), excelled in all professions (Archaeology too), even spent a few hours grinding some Exalted Reputations for BC and WotLK factions and earned some rare achievements.
As she was finishing up her Pandarian campaign, I kept thinking more and more and more and more: damn, I'm losing almost half my WoW experience to not touch the Horde part of the whole cool story. And so my Orc Hunter "Salash" was born.
And then it was just a growing snowball. I've found that playing a different class and race doesn't just open you up to what's going on behind the doors (or skins) of the Horde/Alliance races. You start to understand other players better, find out why they don't cast required items in raids or dungeons.
Also, it's fun to test out new classes. Blizzard really made it so that playing one specialization or another feels completely different. I can't forget how I lost an epic battle with a little turtle vs Micromantica when she tried to cast fire spells!
I've tried almost every spec and class and discovered two things:
1) I like DPS. Since I'm in the story all the time, even in raids, I like going through PvE challenges more or less seamlessly. Tanking didn't appeal to me and I was an average healer, so I eventually switched my druid to casting (btw, sun and moon blasts are the coolest spells in all of WoW - BAMM!).
2) I discovered that melee is no more complicated than ranged DPS - and I was afraid to start a warrior for a long time.
So far I've struck a balance between Horde and Alliance - 5 and 5. Because I think it's fair :) Everyone now represents different races, classes and professions (with minor exceptions of course). They all cover all the class/profession combinations that I thought were cool - and I won't be developing any more chars. 10 is already enough.
Evolving them all is a complicated affair. You happen to run the same quests time after time - especially in the Cataclysm part. It's tiring. But I try to guide them in their own unique ways, weaving their own unique stories according to their race and class. The druid is happy to help with the Hyjal. The hunter is happy to quest Heming Ernestway... Well, it's all fun in the end - since you learned the main plot threads with the first character, you can now invent paths for the others.
