I don't think that there is any ranking system to  categorize colleges as best or worst in Nepal. Ranking depends upon what type of factor you're looking for. Best for success result, best for games, best for resources, best for infra structure, best for teacher to student ratio, and so on are some of the areas that should be rank separately. I dont think that you could find such sight that has an answer to your question but www.afterslc.com has a number of lists of college and their information. It might help you some what.