I have written two sets of examples below. I made up the A version and my non-native English speaking friends did the B version as a revision.
(1a) May is currently studying in university.
(1b) May is currently studying at university.
(2a) Jack met his wife when they were in university.
(2b) Jack met his wife when they were at university.
My friends seem to like "at" more than "in". Please give me your opinion. Thanks a lot.