Over at Nikki Stafford's blog she is discussing the last two episodes of Buffy season 2. Much of those episodes involves a lot of suffering on Buffy's part. While reading the discussion I thought about the things Buffy has to give up as a result of her duty as the slayer and specifically something she mentions after she tells her mother she is the slayer.
Something that doesn't get discussed about Buffy is how gorgeous Sarah Michelle Gellar is. When she is telling her mom how she wants a normal life she mentions she would rather be gossiping about boys instead of being the slayer. She would no doubt have plenty of boys to gossip about.
As the flashback points out, she was the Cordi of her former high school. While I'm sure that has its drawbacks, being a beautiful and popular girl in high school has a lot of benefits.
We see the sacrifices she makes as the slayer when it comes to boys like Owen in the first season, the guy in the third season whose name I forget, and Riley. She shuts out the normal guys (which Riley was initially and is willing to be at the end of their relationship) and thus is only available to the guys she encounters in her line of work. And those guys tend to cause her a lot of pain.
I doubt Joss chose SMG without taking into account her physical attractiveness. If Buffy were an average looking girl or a social outcast like Willow there would be fewer things she had to sacrifice in order to perform her duties as a slayer.
Though on the other hand, she might not have attracted Angel in the first place. And that might have saved her a lot of emotional turmoil.