I actually tend not to play in Sunset Valley, preferring the other towns. Not to say I don't like it, just that I prefer the other towns. That being said, my go-to towns include Hidden Springs, Monte Vista, and Bridgeport.
In Hidden Springs, my favorites are:
Ryan Anderson, combine him with Jess Willow and their children are stunning
The Freespirit Household. Nicholas Riverview has to be my favorite townie. He holds a soft spot in my heart for being the founding spouse of my Immortal Dynasty and his genes look good on girls or boys. See above for Jess and Cassidy's green skin is great
Star Shue, she had a bunch of kids with one of the dynasty spares and they were all adorable
For Monte Vista, my favorites are:
David Haynes, his eyes are dark and his body is awesome. He's also the founding spouse of my current legacy and his children are fantastic
The GilsCarbos, and the Rossis. Their children are great and have since married into the family
And then there's Bridgeport:
I've played two or three games there.
One of my favorite townies is William Fangmann. I can't help it XD I like the chiseled cheek bones and the body. Plus, I like the look of his kids for the most part
I also like Elvira Slayer, though it can be hit and miss with her
Oh, I know these aren't technical "townies" in the traditional sense, but there are a couple Sims from University that have produced some beautiful children.
One of them is Ray Wise, part of the Nerd Group. His daughter with one of my Sims is actually one of the prettiest I've had in game
The other is Jeffrey Dean; another knockout, plus a "bad boy" so it's fun.
I don't know if I have any least favorites; I'd be willing to test just about any relationship lol