If I’m honest I usually choose Kaiden. I don’t want to start the whole ‘Ashley is a space racist’ argument on Lemmy but I didn’t like her attitude in the first game. Kaiden may be a bit bland but a good lad. You’d be okay with him marrying your sister.
It used to be Ashley was my choice to save. She was my romance option for most of my ME1 runs. So it made sense.
But for whatever reason her voice acting in ME3 grates on my nerves. “Are you sure you’re not with Cerberus?” Repeat ad nauseam. Gah, I hate it. Now she dies every ME1 run.
Plus Kaiden is far more useful for my play style I find. Dudes way better than Ashley.
I wasn't even sorry to let Ashley die. She was condescending, hostile, and antagonistic for no real reason. And she's supposed to be a love interest? If you're playing anything but a full renegade, it's hard to imagine she'd even like Shepard.
Kaidan's characterisation fits better regardless of your Shepard's alignment, he's a more useful squadmate in general (especially in ME3), and he's better voice acted.