Hoping my admittedly-biased perspective helps; I’m a sophomore engineering student at ND.
If you haven’t had a chance, come out and visit both campuses. I fell in love with ND as soon as I arrived on campus during my senior year of high school, and have had an amazing experience so far. I didn’t apply to Purdue, but I have had several friends go there. For what it’s worth, two are still at Purdue but dropped out of engineering, one transferred from Purdue to Minnesota, and one is still in their engineering program.
I could list everything that drew me to ND (and if you have more questions, feel free to hit me up), but I have finals on Monday and should be studying - so I’ll sum up two of the most significant.
The professors here are absolutely fantastic; you’ll come to appreciate the quality of instruction in almost every class. Even in the larger classes, there are plenty of opportunities to get personal attention / meet with profs about coursework, research, or pretty much anything. Generally, classes are quite a bit smaller at ND than Purdue, which I found to be a huge benefit. In a freshman engineering course, my prof had previously worked on robotics with NASA on the Mars Rover, and my current physics prof has worked at CERN in Switzerland on several projects. There are some all-star researchers and instructors here in STEM fields - probably in every field, but I’m in mostly technical classes at the moment.
You’ll have opportunities at ND that you won’t get anywhere else - even Purdue. If you’re interested in research, most professors will consider taking you on even as a freshman; I did some research work as a freshman and know many others who did as well (and still do). Internship placement is fantastic; ND’s reputation and the connections you will make give you an advantage in many situations. I managed to get a technical internship for this summer and I have friends who will start internships at Microsoft, Google, Deloitte, GE, and Textron this summer, among many other places.
In terms of rankings, I don’t feel undergrad program rankings are as accurate or important as others may believe. Engineering rankings for undergraduate programs are heavily based on research quantity and quality - which is important, but it tends to reward larger schools (i.e. Purdue, though it’s still a fantastic school) and schools that have highly rated graduate programs. Notre Dame’s graduate engineering isn’t its strength in terms of research output, which (fairly or not) influences Notre Dame’s undergrad engineering ranking as well. For undergrad, there are two things that I think matter than anything else - quality of teaching and reputation. ND’s reputation as a whole is world-class, and though quality of instruction is harder to quantify, I believe the engineering professors are among the best of any program.
Feel free to post any other questions you have - I’d be happy to answer them.
Take this with a grain of salt, as I’m obviously biased toward ND as a current student, but these kinds of perspectives helped me a lot during the college search process, and I’m hoping I can repay the favor.