I have a fairly low tolerance for good defenders getting beat. On the other hand, I'm always telling my girls (until I'm blue in the face) that the offensive player always has an advantage because she always know where she's going to cut, and the defensive player is always a step behind. That being said, I'm always going to put my best defender on the other team's best offensive threat, unless there's a reason that I don't want that matchup—be it height, or speed, or whatever. In the college game, though, it's a lot easier to make up for those disparities.
Right now, I'm teaching my kids team D, which has been really frustrating for them, because they're used to being focused on a single player for the entire point. I'm seeing the light bulbs gradually go on, though, and I'm going to have them use it at a tournament in about a month.
For this situation, I will let them get beat a few times before I try something else, because I want them to learn what they should be doing and what the field looks like if they're doing it right vs. if they're doing it wrong. I'm definitely harder on the ones who know what they're doing, though, for that very reason. They know what they're supposed to be doing right, and if they're out of position, I'm going to ask them to tell me what they did wrong, and have them keep guarding the person who's beating them until she's shut down. Also with this team, I'm a lot more likely to mix around strong and not-as-strong defenders because I want the up-and-coming ones to cover a better player, anticipating that this will also make them better defenders.
I think it superstar matchups depend on what kind of player the superstar defender is. I'll use Danny (Quarrell, from Portland) as an example—he's one of the best defenders, hands down, but you don't really want him guarding Nord in the endzone (though he probably has ended up doing so at some point).
I want him guarding BLW instead, because I want him to prevent one of the game's best handlers from even getting the disc in the first place. And because the height matchup is a lot more favorable. On my college team, my best (smartest) defender is also "vertically challenged." I will put her on the other team's best handler and leave my taller, more athletic players to guard the deep threats, because there are fewer players in the college game who can put the disc wherever they want. I have more confidence that they can shut down a huck play by playing team D than I do that they can get a turnover by each putting blinders on and chasing a single player around the field.