do any of them have a particular preference for masculine vs. feminine appearance, or are they open to anyone that looks attractive?

Side Burn tends to lean more to Feminine figures. But also he's never actually SEEN a femme looking Cybertronian.. only Alt modes who are like... what he assumes femmes would look like

Thunderblast likes more Masculine mechs. The stronger the better and if they can take over the galaxy she's gonna cling to them

Smokescreen.. likes Masc mechs. But he's not picky really if a femme likes him he might hit them up for a date.

Ratchet is more into masc .. probably exclusively