Las Americas is ok if you like the night life but if not, it's vile! Los Christianos is quieter. If you prefer something more verdant, try the norther part of the island.
South Tenerife has some beautiful areas. Scroll down this, sazzie, and you'll get an idea. Adeje's beautiful, with lush areas, ocean views - and luxury housing. http://www.discovertenerife.net/tenerife_beach es.asp
Any of the main areas are alright if you fancy nightlife, but Playa DL Americas is now spoilt.