Historically, the right strategy in Afghanistan was staying out of the place. But it is too late for that, and simply seeing the country fall into the hands of monstrous and brutal thugs like the Taliban would be difficult for the United States to stomach.
American strategy in Aghanistan has focused on quantity and breadth rather than quality and depth. Counter-insurgency, as the eminent scholar Elliot Cohen has noted, "is a valley-by-valley" war. What he means is that success requires an enormous amount of very specific local knowledge about a region. Given this kind of knowledge of tribal structures and inter-tribal relations, as well as the preferences of key individuals, combined with the ability to provide goods that these local leaders want, a dynamic individual can achieve modest amounts of influence. But acquiring this level of knowledge takes a great deal of time (years, maybe decades) and then, when this knowledge is possessed, the influence that can be achieved is modest.
But this may be the only path in a place like Afghanistan where daily life is difficult and societies tend to be cautious and conservative - knowing that change can often be for the worse.
This does not mean that Afghanistan should simply be abandoned to its fate (Afghanistan didn't ask to be a central front in the Cold War), only that the goals should be modest and patience is necessary. The United States and NATO have hopefully acquired the necessary background knowledge and a more modest strategy is far less expensive then full-blown counter-insurgency (although it will require cutting deals with some loathsome local warlords.)
The question is, with the Taliban resurgent, what would it take to make such a strategy viable.This COIN stuff is really hard and takes forever - not having any practical experience I tried to put it into terms a soft suburbanite arm-chair analyst (like myself) can grasp. The Afghanistan of much of the 20th century was a soft monarchy. Kabul was a modernizing city and the country stayed together. Life there was undoubtedly less than ideal, but absolute chaos was avoided and there were at least some options for improvement.
I've taken on this question before. The main alternatives would be to abandon the place, leaving it in the hands of the vicious Taliban and allowing it to again become a source of regional instability. We could just continue to do what we have been doing - but the US doesn't have the resources for a full-scale counter-insurgency and the present policy is probably a greater expense than the benefits it can realistically accrue, plus it gives Pakistan too much leverage over US foreign policy.
The key is to maintain sufficient military capabilities to back up the Afghani forces (and continue to train them - although the prevalence of insider attacks makes this seem hopeless.) But after the Soviets left, the Afghani government held out longer than anyone predicted and with only limited outside support. Could the US back-up a regime in Kabul and work with that government to slowly (glacially) spread its writ across the country. This is probably the strategy that needed to be adopted from the beginning instead a beginning of apathy followed by a period of frenetic attention. This probably the path that should have been followed in exiting Iraq - but did not happen when a status-of-forces-agreement could not be reached. There is still time in Afghanistan to do at least some things right.