It honestly doesn't matter. I got 99 woodcutting with rsbot and i still feel like i cut yews the same speed as i did at 60, so it's all on what you think.
No level is high enough to start cutting yews.
My main has 99 wcing and it takes fucking AGES to get a log.
Botting it doesn't matter, start at 60. But if you do it by hand then don't even do it. I did willows from 30-99. Much faster compared to yews.
But willows have gone down so you won't make the 50m+ that I did.