People attribute happiness to different stages of life. While for some the happiest time of life equals teenagehood, others, however, believe adulthood, with all its great responsibilities, embodies more happiness. Although there is some credit in the latter perspective, I personally would lean towards the former.
The reason why for some the adult years bring more happiness is that during adulthood most people land a job, get married, and form relationships at a deeper level. All these, psychologically, fill life with meaning, and for most of us a more meaningful life entails more moments of joy. However, it is difficult to overlook all the responsibilities of adult life, such as managing expenses, setting aside time to spend with the next of kin, and balancing work and life, which all add up to the stress and take its toll on pleasure.
The teenage years, on the other hand, are considerably more carefree. Teenagers hanging up with friends around the corner is a common sight almost everywhere. This period of life, for most, is full of fun and colorful experiences, which will be remembered for long. The only imaginable challenge for teenagers would probably be mood swings caused by hormonal changes occurring during adolescence, which does not last forever.
In conclusion, adult life, with all its meanings, goes along with back-bending difficulties, and most adults, almost always, reminisce about the sweet old days of the teenage years when they used to be free from the stress and burden of their adult life; therefore, I believe happiness lies with teenagehood not adulthood.