This depends heavily on your market and whether people in it frequent certain sites.
For example, my old dealer group sold nicer foreign new & used vehicles, from Hyundai to Porsche, in Virginia Beach and Norfolk, VA.
I found that our volume-oriented brands like Honda, Toyota, Hyundai, VW, etc. did better on Autotrader while our luxury brands (BMW, Audi, Jag, Land Rover, etc.) did better on Cars.com. The reason wasn't the brand. It was a price point. It took me a while to realize that Autotrader attracted shoppers looking for less expensive used cars. Cars.com attracted shoppers willing to spend a bit more in our market.
I had to test them all and hunt for the patterns. There isn't an easy answer. However, I can tell you that if you work with your own database and use the right tools, you can get quick conversions.