This is going to depend a lot on your definition of "manifest destiny." To many people, the idea of manifest destiny is similar to aggressive imperialism and this would not be an either/or sort of a question.
Manifest destiny was the idea that God had essentially given the US the right to expand its territory. The US deserved this because it was a superior country. If God has given a country the right to expand, then it is appropriate for that country to engage in aggressive imperialism.
If what you are asking is whether US expansion was motivated by good or by the desire for power, I would argue that there were elements of both but that the desire for power was paramount. The US, for example, actedly more humanely towards its Filipino subjects than Europeans did towards "their" Asians. The US even promised the Philippines independence after a few decades of American rule. However, the main point of taking the Philippines was not to help Filipinos, it was to gain access to resources and to have a military outpost in Asia. Therefore, US expansion was more about aggressive imperialism than about helping others.