Ashley: Nickleback and country
Jacob: pop genre, rap, and songs about cheating
Nickelback?? Is that supposed to be a diss
And LOL about Jacob.
Garrus's Shadow Broker dossier already shows that he's partial to EDM, but I imagine most of inter-galactic society is by default. For Earth stuff, he always makes me think of classic hard rock, like 70s, 80s. Led Zeppelin and Rolling Stones. Maybe some 90s, like Foo Fighters.
Vega is uber-West Coast. West Coast is either punk/garage rock or hip hop. He is definitely hip-hop.
I imagine Kasumi would have a soft spot for Lana Del Rey. Lana is all about that tough-girl street smart swagger, but also extremely sensual, romantic, with a penchant for all things vintage, old-school Golden Age Hollywood glamour. With Kasumi's badassery and love for hardcopy romance novels, I feel like she'd be a sucker for that type of thing.
After seeing Tali try to pull off love songs after Fleet and Flotilla, I can't help but think she'd be a R&B girl. I can imagine introducing her to Beyonce or Alicia Keys and hear her say again, "so many feelings".
There is something old-school and classy and romantic about Kaidan, but that might just be his hair-do lol. How about anything from Justin Timberlake's 20/20 album? Bruno Mars?
Samara- definitely new-age music. Like Enya?
@OP - I'd imagine Liara is the last one to blast 'Barbie Girl', even if she went 'nuts' lol. She's pretty classy, elegant, and calm. Even though she's still maiden, she's clearly not the crazy eccentric type of maiden asari. She clearly likes serene instrumental pieces as seen in her piano Citadel DLC scene. I want to say classical, but nothing like Mozart or Bach. Something from the Romantic Era, but nothing grandiose and extravagant. I'm thinking Debussy, like Claire de Lune.