1. Answer: It depends on everyone's taste and these rankings change all the time. According to RankMyPorn, at the moment, the top ranked Under 25 Male Pornstars in the world are: Marco Rivera, Giovanni Francesco, Charlie Dean, Jason X, Sabi, Thomas Long, Enzo Bloom, Johny, Eric Hard, Bambino, but these will change based on what people vote.
2. Answer: It changes. You can see the latest rankings on RankMyPorn.com and also vote on it for free.