They're essentially the same GM crossover model with GMC vs. Buick badging. The Chevy Traverse and discontinued Saturn Outlook models are also GM corporate siblings to the Buick Enclave and GMC Acadia. IIHS crash tests earned Good ratings for frontal and side impact tests for these models:
http://www.iihs.org/ratings/rating.aspx?id=977 and
http://www.iihs.org/ratings/rating.aspx?id=1021 I can't get NHTSA's site at safercar.gov to load to try to pull up NHTSA's crash scores, but you can also look at informedforlife.org to see a composite safety score that pulls from the IIHS and NHSTA crash tests.
I know we have several members with these GM crossovers who can chime in on carseat friendliness and you can probably get some ideas from the 3 across thread or the Radian install thread. Testing carseat installations during a test drive is also highly recommended before any vehicle purchase.
I believe the second row's headrests can pose a compatibility challenge for some forward facing installations, but seem to remember workarounds by reclining the vehicle seat a notch or two or maybe a way of removing the headrest? These models have dedicated sets of LATCH outboard in the second row. GM doesn't allow borrowing to do a center LATCH installation in versions equipped with the second row bench seating (some versions have second row captain's chairs, and some have second row benches with 3 seating positions). There are top tether anchors for every second row seating position and for the third row center seating position.
Between the two they've narrowed down the choice to, go with whichever model meets their budget and preferences the most I'd say. I'm not sure which version is more spendy between the GMC and Buick versions, but I believe the Chevy Traverse has a lower starting MSRP. I also don't know if there are any changes in store for the 2011 models, and 2010 models are probably much more negotiable price wise as they're reaching the close of the 2010 model year now. :twocents: