This is, of course, simply a matter of opinion because there is no way to objectively measure the benefits of the testing or its costs. I would argue, though, that animals are a lower form of life and that human life is so much more important that therefore scientific research using animals may be acceptable.
Animals are clearly a lower form of life. We accept that when we use them for food or when we make life and death decisions about our pets. Therefore, it can be said their needs are less important than needs of humans.
When medical testing is done on animals, it allows humans to live better, healthier lives. If people's lives or even their health can be saved, that is much more important than the lives of animals. As long as the testing is necessary and is humane as possible, it may be argued that the benefits to humans outweigh the fact that the animals are having to suffer.
Please follow the link for an opinion piece on this issue as well as links to many essays exploring other facets of the issue.