I just moved to Holland MI a few weeks ago (Holland is 30 minutes from GRR), but used to fly into GRR when visiting the west side of the state and it will be my airport for future trips.

I think, for the most part, you're going to be connecting - whether it's DTW or ORD, so if you're Plat w/ AA you may want to consider staying with them. I think they run RJs to/from ORD. I'm a UA flyer & am sticking with UA, as they have several flights a day to ORD & DEN. Given the NW/DL merger, that's also a consideration for you and maybe a strong one, given the NW part.

Re: taxis. I usually do rental cars, so trying to remember if any taxis are by the curb. I think they have them, but haven't paid attention much & also outside the airport is under construction at the moment, as they're building a large enclosed parking structure. You might want to call the airport & ask re: taxis. My 'guess' is that they're cash only.

GRR is a pretty small airport (especially compared to ORD), so no 'fast-lanes' or 'hidden checkpoints' that I'm aware of. I've not encountered too many backlogs at security, but that could be because of times I've been flying.

FYI - right outside of security is a small glassed-in room that has some chairs and counters that you can use for bizness. It's underwritten by Steelcase I believe. If I get to the airport early or upon arrival while waiting for luggage, I usually pop into there to access free wifi/make some biz calls.

Post here or PM me if other questions re: GRR area.

Cheers.