Having grown up in Lansing, off to Kzoo for college, and now residing in GR with family still in Lansing, I'd say GR hands down. It's downtown is much better, the job market is much better, and the neighborhoods are much more eclectic. In addition, Cooley's campus is in a national historic district just South of downtown GR called Heartside, with pubs, art galleries, the arena, coffee shops, Urban Institute of Contemporary Arts, Avenue for the Arts, and quite a few loft apartment projects. In addition, with GVSU's downtown campus, Kendall College of Art and Design, WMU's GR campus, MSU's med school moving to downtown Grand Rapids, and Calvin's art programs all downtown, there's well over 25,000 college students downtown at any given time. Add in Aquinas and GVSU's Allendale campus and there are over 50,000 college students in GR.
Here's an old picture I took a few summers ago of Ionia Avenue in the Heartside District, with its rebuilt brick streets. Cooley is one block over to the right in this picture. In the foreground right is the Globe Apartments (factory conversion), and WMU's campus about halfway down on the right. There's a new apartment complex just out of view to the right that is scheduled to open this Spring.
And here is Commerce Ave where Cooley's campus is:
There are a few missions/homeless in this area, but it's becoming more mixed with all the redevelopment/historic preservation going on.
Hope that helps.