I have received an admission offer for a PhD at a prestigious US university. However I am also currently working in another lab outside the US with a potential to also receive PhD admission there.
I think the deadline to respond to the US school is April 15 but the professor asked me politely to give an answer within a reasonable amount of time, also my former supervisor (which has no interest in the matter) suggest not to string along the US school and try to make a decision well before the deadline.
I feel it might be unethical to wait the last minute because I respect the professor and he might lose good potential candidates. On the other hand I want to wait and see if there is a concrete possibility of pursuing a PhD at this other place.