Happy_Person,
There are no specific easiest way to get US visa, it is always 50/50 chance.Your brother does not get visa unless he apply, there is always a risk of not getting visa stamped on every category. We have to be prepared to convince consular that we have no intention to stay in the USA. For Nepalese most popular are visitor and student visa. Since your brother already has MS and wanted to be here other than student visa ( since you have good financial support for him, there is more chance of getting F1). Or if he wants to be here soon or does not want to go to school, applying for visitor visa does not sound bad too. As everyone suggested above he has to prove that he has strong ties back home. What I heard was if some one has traveled overseas there is more chance of getting US visa. If I were you I would ask him to visit some places like Singapore or at least some tourist destinations.
Other than that everything depends on luck and mood of consular. Best of luck !

Hope it helps.