I’d be a Slinky.
I saw this thread title and thought “Slinky!” immediatly, but you beat me to it. Damn.
Right now I think I’d be one of those remote controlled kitties… with dead batteries.
A teddybear, of course. 
jayjay
legos.
ohh, the legos.
rubber duckie.
Vibrator. What other answer could there be?
Okay, maybe a teddy bear or other beloved stuffty if we need to be less graphic.
A Mr. Potato Head doll. “Don’t forget your angry eyes!”
I’d be a balloon.
Hey! No begging for straight lines! 
jayjay
I’d be a Barbie
But, I am a toy.
Nooooooo!
That is an unattainable goal, and destructive to little girls’ self image.
Me?
I’d be “The Incredible Hulk”.
Peace,
mangeorge
My collector Titanic Portrait Doll from the Franklin Mint.
Let’s see, I’m rather quiet until I get to know people, then you can’t shut me up. I desire cuddling, but when I want to be alone, I want to be ALONE! I could sleep for days at a time, only getting up to shower or eat, if I actually had the chance.
Crap…I just described a Furby.
Maybe, but ya got admit (just like the t-shirt says) that bitch has everything!
An old fashioned long hair teddy bear, gently worn in all the right places.
Army men, and lots of them. Especially the kind that you could order from the back of a comic book, before comic books cost you $10 each…
I’d want to be a kazoo, so that every time people put me to their mouths and both hummed and blew, they’d be making music.
Cartooniverse
I’d be a Koosh Ball. Everyone loves a Koosh Ball. Everyone loves to handle, play with, and otherwise fondle a Koosh Ball.
Plus, they make people happy, so they’re just like me!