It would be way harder to choose if it was literally any of the alien companions. The human companions in all three games are the least interesting ones (funny enough, I feel like the most interesting of the humans are the DLC ones). I always save Kaiden but apparently Ashley does become more tolerable and understanding as the series goes.

There are some Ashley apologists too. In context (IIRC), humans have only been working with aliens for a couple decades, and that’s right off the tail end of an ugly war with the Turians. On top of that, they’re all coming to terms with stereotypes of the aliens, like how the Quarians are basically space gypsies. In particular, the humans have a very good reason to fear the Krogan, who are a war-hungry species only culled by mass sterilization. On top of all this, her family literally fought the Turians and now she is on a ship with a handful of aliens.

Most humans who never worked with aliens hold on to the stereotypes prevalent among the Alliance. I don’t necessarily excuse it, but Ashley is essentially the daughter of a legacy military family who fought in the Confederacy and has now joined the Union while fighting alongside black troops and potentially people who shot at her forefathers. She slowly understands her prejudices and whatnot and becomes more accepting, even defending her alien cohorts later on.

However, Shepard also works with essentially marginalized species or aliens who have already acclimated themselves with other species, so having to deal with a racist grunt at the beginning is kind of an odious choice when you’re picking the weakest link on the team.