Seven-of-Nine is my first choice. She's so grim and serious all the time, yet has an awe-striking smile that she reveals on special occasions. She could benefit from a hearty laugh.
Kes is second choice, as Jennifer Lien has the sexiest voice in Hollywood.
B'elanna Torres might be in need of a good laugh, but Klingons have nasty feet. Their insteps are covered with armored ridges that match their foreheads. Ick.
I can't stand Janeway's normal voice, so I don't want to hear her gibbering incoherently. "I'm not prepared to accept that... I'm not prepared to accept this..."
Seska, being a Cardassian, has scaly reptillian skin that is not only not ticklish, in all probability, but not much fun to touch under most circumstances.
Might I suggest some alternatives?
The Delaney Twins - Tom Paris and Harry Kim were always talking about hooking up with these two from the science labs. We finally saw them late in the series (in one of Tom's B&W "Captain Proton" fantasies on the Holodeck) and it was worth the wait.
Ensign Samantha Wildman - She married and had a child with a spiky-headed Ktarian, so she could be into all kinds of kinky stuff.