[Linaro-uefi] Best baseline for new platform support?

Hi folks, I'm looking at getting TianoCore/EDK2 running on a simulated SoC platform using a Cortex-A53 processor, which should bear some resemblance to SBSA. I'm a bit confused, though, about which EDK2 repo/branch would be best to use as a baseline at the moment? Also, I'm guessing OpenPlatformPkg is the way to go now for new ARM platform-specific code, rather than ArmPlatformPkg?

Cheers, Scott.