Note that UIUC and Purdue take different approaches to handling departmental capacity limitations.
UIUC admits students directly to major to mostly fill departmental capacity with frosh admissions, with a small number of spaces available for competitive admission for undeclared students later. Students in the major need only earn a 2.00 or 2.25 technical GPA in college to stay in the major (see http://catalog.illinois.edu/undergraduate/engineer/#TechnicalGPA ). However, students wanting to change to a different engineering major may find that the process is highly competitive and requires a much higher GPA, depending on the major. So UIUC may not be the optimal choice for an undecided engineering student or one who is likely to change major (actually, this extends beyond engineering at UIUC, since many majors, not just in engineering, are capacity limited).
Purdue uses an FYE program, but does not guarantee that all students who pass the FYE course work can choose their first choice major, due to capacity limitations. What it means is that most students at Purdue are likely to face a higher GPA threshold to meet than UIUC students who were directly admitted to the major and will not change major, but a lower GPA threshold to meet than UIUC students who were admitted undeclared, or who decide to change major.
Which is better (assuming affordability is similar or not a concern)? It depends on the student. A student who is certain of his/her major and is directly admitted to it at UIUC will have fewer worries there than at Purdue. But an undecided student, or one likely to change major, is more likely to find Purdue to be more accommodating.
Of course, if the student is admitted to Michigan engineering, then Michigan is the answer, since the FYE student can choose or change to any engineering major if s/he maintains C grades and a 2.0 GPA, due to the lack of any capacity limitations imposed on enrolled students (looks like the purposely admit fewer than the maximum possible frosh engineering students in order to have enough reserve capacity in each department to allow for non-competitive major declaration and change).