Hi there, im 33 now (getting on!!) but have been a requent visitor to teneife PDLA since i was 19 (been 13 times now) and always used to go for the nightlife (although thats all stopped now im preg!!) just got back from spending xmas and new year there and its a brilliant as ever.
Places i would recommend are as follows - all are within a 10/15 min walk to main drinking areas and apartments rather than hotels. Assuming rightly OR Wrongly your in your twentys and want apartments. If your looking more towards hotels let me know.
Prob one of the best lot of apartments in Las Americas are the Colon II (only thing is only avail through thomsons i think)
http://www.tripadvisor.com/Hotel_Review-g562820-d641498-Reviews-Colon_II_Apartments-Playa_de_las_Americas_Tenerife_Canary_Islands.html this has reviews on them
Slightly lesser quatity than there you have Califonia - have stayed here myself - loved it = basic standard apartment = good reception - quiet on evening so can catch your sleep, next to a supermarket, and 10-15 min walk to bars is a good one as you pass several good bars en route you can stop and have a cheeky one at.
Just came back from stayin at the Andorra apartments - and next door to them is the Parque de la Paz - both are fab and again 10-15 min walk to main place, these are set in a great area - loads of fab restaurants at the Safari centre which is about 3 min walk away - and also a 2 min walk to a strip of bars which are great for starting off in with good bands on before you hit the Linekers, Tramps etc
Would stay away from any of the below (been there done that wouldnt recommend anyone to do it!) Paraderro!!, Parisio del sol.
A popular choice on 18-30s is the Piramades - these are far enough away from the main nightlife but do have reports of being noisy during the night (have friends how have stayed there loads over the years and they say rooms are great as is location and apartments but if you want a good sleep every night then dont bother.
if you are doing private let apartment rather than package deals check out any of the Parque Santigo - there ace - stayed in the Parque Santiago 2 a couple of years ago - best accom ive stayed in in tenerife - but sure these are just private let rather than package - although i maybe wrong as its been several years since i done a package deal
hope this helps - any more info with PM me
Shaz