Just My $.02! Go with Ash! I was researching this a few years ago and found that body builders in the UK will not use oak, they used ( and use ) Ash. Now the species of Oak varies, for instance, I don't believe that Britain has what we call "Live Oak". To this day, Morgan uses Ash in all it's cars. There maybe several reasons for this. Oak tends to splinter into long wooden daggers when it with sufficient impact. This was noted in the days of wooden sailing ships when some of the most dangerous things were flying oak spears on their cannon decks. Ash is a much finer grain and that makes easier to get and hold dimensions better. Also, I believe Ash is somewhat better at moisture resistance. This is not proven, only suspected. I believe Oak will draw up more water and there for there will be a greater distortion and loss of size due to water absorption.
Terry