Twinbrook and Appaloosa Plains seem pretty comparable in size to Sunset Valley, and they're both nowhere near as overused. Placing extra lots is a bit of a nightmare in Twinbrook, though there is space near the Curious home, the military base, and Juan Darer's house. I can't say as much for Appaloosa Plains due to a lack of experience there.
Didn't know about the routing in AP, though. Twinbrook runs like a dream on my pitiful set-up, so it might be a consideration for you too.
Moonlight Falls is the smoothest running town for me, and there is plenty of extra space for new lots. The population is tiny though, and most of them are supernaturals, but it's possible to do an immortal dynasty there. The combined rabbitholes are nightmarish for opportunities, but you could rely on skill ops that aren't tied to rabbitholes. Maybe.