The system in the Mazda 6 sedan was the most distracting, the study said.
The study examined voice-activated systems in 10 2015 vehicles on 257 drivers and three smartphone systems on 65 drivers.
Researchers found that potentially unsafe levels of mental distraction can last for as long as 27 seconds after completing a distracting task in the worst-performing systems studied.
The analysis found that all systems studied increased mental distraction to potentially unsafe levels.
The best systems, like the one in the Equinox and Buick LaCrosse sedan, "had fewer errors, required less time on task and were relatively easy to use," researchers said.
Each system was rated on a mental distraction scale of one to five, with five being the most dangerous.
The Equinox and LaCrosse were given a rating of 2.4. The Toyota 4Runner SUV was given a rating of 2.9.
The Mazda 6's 4.6 rating is considered to equal a "very high" distraction level, similar to updating social media while driving.
"The lasting effects of mental distraction pose a hidden and pervasive danger that would likely come as a surprise to most drivers," said Peter Kissinger, president and CEO of the AAA Foundation for Traffic Safety, in a statement. "The results indicate that motorists could miss stop signs, pedestrians and other vehicles while the mind is readjusting to the task of driving."
The foundation says that automakers should design systems that are no more demanding than listening to the radio.
Edmunds says: Car shoppers who value connectivity will want to take a hard look at this new study, since it underscores the fact that hands-free driving isn't risk-free.