I use Sweetspot PCI RGB capture card. It can record Composhit, s-video and RGB!!!!! I record mega drive with rgb and enjoy the best colors and image quality.
I just use scart splitter. I input rgb scart to scart splitter, then output with scart-3rca cable. Also dont forget to wire compshit to Green in the scart plug to get RGsB signal because then Sweetspot wont get the RGB signal properly because megadrive gives sync on composhit.

