If you prefer youngish, then SL is a good choice. You can't go wrong with Lucy or Coco and lots of guys swear by Renee (but I've never seen her before). In my opinion, the massage quality at SL is a notch below some of the other semi places but at those places, the ladies are usually a bit older. Xtc guy will disagree with me here but I'll go out on a limb and say I'm pretty sure I've been to more semi places then him
La la Land near Warden and Denison apparently has some youngish MPAs as well but I've never been there yet (it's on my TDL). It's been reviewed here recently so you can search for them.
If you don't mind places where there's a mix of young and older, then Just Relax is a good choice. It's basically next door to SL so you can check out both. Serene Ocean at Leslie and Hwy 7 has a good mix too.
Suko also has a good mix too but I find them more tip hungry although I hear that's been improving lately...