There really is no such thing as a "mini", etc, just a poor pup that's been bred to be as tiny as possible so as to make as much money as possible for the breeder.
The AKC breed standard simply states not more than 7 lbs, but anything smaller than around 4 lbs and health issues start cropping up; obviously, the smaller the dog, the more series the problems.
I have a Yorkie who just makes the 5 lb mark. These dogs are very, very smart, but also fairly needy. Jasmine has learned over six commands that can be given by either voice or hand signal, as well as several more by voice alone. She responds instantly to "Stop!", she knows to sit and wait for permission to take/eat a treat, and she pees and potties on command (I swear it!).
I have had various other pets in the nine years I've had Jaz, including an 85 lb black lab (my ex's), birds, cats and rats. She gets along famously with all of them. I've never met such an intelligent, loving dog.
On the down side, she's so small she needs assistance getting on the couches and beds - and she's not happy unless she's up there with me. She won't make a fuss, and she'll find someplace else to lie down, but that's only because she's a good girl, not because she's ok with it. I have doggy steps all over the house because I can't stand to see her sad.
But the biggest thing, and the only thing I would warn potential Yorkie owners about, is they are incredibly hard to housebreak. That is why Jaz is trained to pee and potty on command - it was a last ditch effort, after 18 months of trying everything under the sun, to end the peeing in the house. Thankfully, it worked, and we've never had an accident since (not even when I went away for 28 hours and my mother FORGOT to come by and let Jaz out!).
Oh, and I wouldn't recommend that Yorkies be in families that have small kids, only because they're so small themselves they get hurt easily.
Just my two cents worth.
