Where do you think HP, Dell, etc buy their drives?
Yep, from the company that offers them the best price on that particular day, and the HD's they get will be no worse or better than what you can buy.
So, the HD in your laptop is most likely a 3'rd party drive, only it's bought by the company that made your lappy, rather than by you

The other option being that said company actually manufactures hard drives as well, Toshiba and Fujitsu are the only companies that do this as far as I know(Does Hitachi make lappys?).
That said, you'll get lots of answers depending on who you ask, but the only way to get a statistically sound answer would be to gather statistics from HP, Dell, etc, who actually handle sufficient volumes of them.
Needless to say, they'll never tell you, so just buy what seems good to you.