With a very small exception, all 1st gen Equinox were powered by the 3.4L V6 and an Aisin 5-speed trans. The small exception is the Equinox Sport that was produced for one or two model years that was equipped with the 3.6L HFV6 and GM 6-speed trans.
The 3.4/Aisin combo is pretty robust. The 3.4 has a dry intake manifold and doesn't have any of the intake gasket issues that the earlier 3.4 had. The Aisin trans has shown no common problems.
Stay away from AWD. The rear drive unit is a bit fragile and expensive. Electric power steering is overassisted, completely devoid of feel, and sometimes a little flaky. In typicaly GM fashon, front end parts aren't all that tough and rattles are common. Sway bar end links and upper strut mounts making noise are usually the cause. Wheel bearings are a common replacement item too.
My in-laws have a little over 125K miles on their 2005 AWD Equinox. It's had it's issues. Nothing major and it's never left them stranded. It's also had no maintenance except for oil changes, if that tells you anything about the type of vehicle owners they are.
I owned a Saturn Vue for a while (my wife's). Close cousin to the Equinox, except with a Honda powertrain (which was both the best and worst part of the vehicle). 70,000 miles and the results were similar. Had some issues, but nothing major.