I'm a fan of any and all vanilla scents--vanilla, vanilla select, vanilla ice cream, sharp vanilla, smooth vanilla, French vanilla, vanilla sandalwood, and anything else all by themselves in soap.
Your personal preference will vary, however, and vanilla tends to combine well with most earthy or fruity scents.
Keep in mind that the vanillin will discolor your CP soap quite severely, so make sure you don't bother with a delicate color. It's going to go brown. My sharpest vanilla scent actually turns soap somewhere between brown and mahogany depend on how much I use. I've learned to love the color...