If you are an international student and dint have the good fortune of making campus visits, its best to talk to graduate students in the department. Gatech is definitely very reputed for engineering. ND's Chemical engineering department also has some awesome faculty.
About students getting pushed hard, qualifiers can be a little/very stressful in any school so I dont think that should be the sole deciding factor. So check out the research groups you want to work with and talk to/mail a grad student if you can. Different applicants have different priorities when they take a call on accepting an offer from a school- other than the program, ranking and faculty check out factors like location, weather, student satisfaction etc.
Both are great admits- congratulations!
I too have an admit from ND and will most likely be going there this Fall.