Q:3rd country visa transfer

i'm sorry to bother all.my visa type is J-1 visiting scholar.i want to persue PH.D in u.s.But now i don't want to get waiver from China.I will go to the 3rd country to change my visa type to F-1 or j-1 student.Is there possibility to directly change to F-1 visa without waiver?which one is more easier,f-1 or j-1 student?And i plan to get offer from the other university,will these affect my visa transfer?
thanks for your reply.