I think it depends on how the students in your university would be chosen as a pan pal, by the student in the US or by the profs in your department?
If the students in the States decide, they might choose the students who share common interest or hobby.
If the profs are the one to decide, it could be either a student who excels in English or the student who's level is good enough to communicate with a native speaker but still needs improvement. You can try to figure out what exactly they are looking for then write your self-introduction and strengthen the part they are most likely to appreciate.