Yrovi, my main, a Forsaken warrior; Untainted, Blood Elf rogue; Eruza, Troll priest; Xapha, Blood Elf mage; Mål, Blood Elf paladin; Dahr, Orc hunter; Phedré, Forsaken warlock; Purah, Blood Elf death knight; Xyno, Tauren druid; and Whitestone, Tauren shaman (19 twink at the moment, although not a great twink)
I love each and every one, even if I don't currently play them all. I change my focus about every two months, I guess, usually choosing a pair of alts to play when I need to step away from Yrovi. Lately it's been Mål a great deal, with a bit of my rogue thrown in now that he has no rested experience, as she's just starting the Arathi Highlands area. Not my favorite place to level, but not terrible, either, and I haven't been there in ages.
Because I have all 10 slots filled (plus more toons on other servers), and only one of them is at the level cap, I find it hard to figure out what's going on with each of them at any given time. That's why I have Altoholic, an alt management add-on. It's pretty fantastic. It allows you to see each character's professions, auctions, bag contents, gold, etc. It also shows you how much rested experience each toon has, and what amount of experience they are at before the next level. That's got to be my favorite feature right now. I like the boost to my experience as leveling goes super fast when you're rested up, and knowing which toons are closest to leveling makes choosing which to play a little easier.
It's great for professions as well. If a profession recipe drops on one toon, I can tell very quickly if any of my alts can use that recipe and then mail it to them. If I have a toon that isn't high enough level to use it, the tooltip on the item will let me know how many skill-ups away until they can. I'm able to manage their professions very well, now, and I'm actually able to level them without having to buy too many mats as I can shift things around when I get random items from chests and such. For example, Mål has jewelcrafting. He is currently needing silver, a fairly rare metal, and it is pricy on the AH. I popped on Altoholic, and used the search feature to find Silver. It looked in all my alts bags and just happened to find a large stack of Silver bars in Yrovi's bank. I had forgotten about them, and they've been rotting there. Perfect. He got them and leveled further in Jewelcrafting. Yrovi opened a bank slot. Win-win.
Basically, it's very informative. If you have a ton of extra characters, go get this add-on. It will save you some grief.