The more I think about it, the harder a question I think this is to answer. If I’m playing a tournament match in standard counterpick format, I’m never going to spend much time in these match-ups, unless I win against someone who isn’t interested in counterpicking me. If I lose, I’m immediately going to switch to one of the characters I feel gives me the best possible odds to win the set.
Based on recent experience, I think Grave/Oni is probably very close to even. I don’t have a ton of experience in it though, so take that recommendation with a grain of salt.