RHYHORN
You can't say it would get its ass beat a lot, because it could bring down pretty much all the other pokemon in the poll, barring Cubone.
First of all, just look at it. It's a freaking boss. Just as badass as Aron, IMO. How can you deny how cool it would be to start out with one of these?
In addition to looking awesome, it turns into a beast called Rhyperior. This could go in with the "maturing with the pokemon" theme that was mentioned earlier.
Here's another reason why eventually having Rhyperior would be great.
"From holes in its palms it fires out Geodude."
That's from it's Pokedex entry. It works with the fainting=dying idea.
I honestly can't think of a better starter than Rhyhorn, and it DEFINITELY deserves to be added to the poll. I can defend it more if you want me to.
Copy that. ^^ So it's RHYHORN for me.