Need you ask that question of me? I would be a vicious bloodsucking squirrel with telekenetic abilities that will allow me to fly and destroy all the other predatory animals in the forest…starting with Orion(please go to supernova)Orion.
HUGS!
SQrl
A polar bear.
Or maybe a humpback whale.
Or an otter.
Yeah, an otter would be cool.
Who would want to be an oyster when you could be a quahog? Quahogs were used for wampum, and I find those two words irresistible.
If anyone messes with me, I can whomp’em. (Get it?) During my long, restful life (quahogs can survive for more than 200 years–the longest-lived animals known) I could come up with innumerable great puns like that, in between long naps in my warm and cozy shell.
Well, someone took my answer, but I’d be some kind of bird, preferably near the top of the food chain. Flying would be fun.
``All of your dreams will come true. All of my dreams came true, but now… I have a bunch of other dreams.’’ – Sonic Youth.
Orca
Intelligent, beautiful, graceful and at the top of the food chain.
SDMB’s oldest living female!
Acclaimed author of: No Bad Brontosauri
365 Ways to Cook Sabertooth Tiger
The Complete Idiot’s Guide to the Wheel
I like otters too, Phouka.
I really don’t care, as long as it is at the top of the food chain. 
VB
Some people say that cats are sneaky, evil, and cruel. True, and they have many other fine qualities as well.
A kangaroo.
Sometimes I’m bouncy like a kangaroo…and imagine all the stuff I could fit in my pocket! 
Any connection between your reality and mine is purely coincidental.
why does my razz never work? 
Because you’re not doing it right.
I’m a member of the Bandicoot family, actually - one of the Striped Bandicoots.
— Philipa Psmith Striped-Bandicoot
There is only one difference between a madman and me. I am not a man.
An elephant. They’re beautiful, intelligent, friendly… They’re very social creatures, they take care of each other. I just think they’re the greatest. And there’s not a whole lot of animals who mess with them (except for some humans… :()
A cat: so I can sleep all day, eat, and catch mice(my oldest cat does any way) and pet me lots.
But I’ll only purrr if it’s Squee petting me
kiss
I am a fire whose flames lick and spit at the boundless sky forever desiring wonderous consummation
-me
Cat or a member of the feline family (leopard, ocelot, panther…). Or, if mythical animals are valid, perhaps a dragon.
Your Official Cat Goddess since 10/20/99.
SD chat:
<Jophiel> Kat’s here! the board must be down!
There are a lot of people who want to be birds so that they can fly.
The reason my choice of animals was *me, is that I can fly! You can too! For the price of a well-used car or one ski-vacation to a nice resort (plus some dedication on your part), you can learn to fly an airplane! Just go down to your local general aviation (GA) airport, talk to an instructor, and you’re off!
Then you can be your own animal and fly too.
Somebody already said wolverine, but that’s first choice - antisocial and proud of it
Emode reckoned bassethound (well, the IQ test looked too much like hard work)- but I don’t feel like a basset, more like a dingo
So I’ll settle for dingo
A Bengal Tiger… They are strong and graceful and because no two tigers are ever alike. I like being different.
I really try to be good but it just isn’t in my nature!
WIU Wozman,
That’s funny… “Wallaby” is close to my last name, and my nick name has been JoWallaby for years (I even sign some of my posts with that), but I didn’t even consider wanting to “be” a wallaby.
Dunno why.
Chrome Toaster
Unicorn.
Why?
'Cause 1–nobody believes they are real, so I wouldn’t become an endangered species, AND
2-- all the virgins I could handle, guaranteed!!! :o :o 
It matters not whether you win or lose; what matters is whether I win or lose.
Prose stole mine: housecat.
What a life.
10 Sleep 20 hours a day,
20 pester your human,
30 get fed,
40 take a crap,
50 have a nice leisurely scratch,
60 look out the window at the leaves blowing down the street,
70 goto 10
A committee is a lifeform with six or more legs and no brain.