The junior novel is low in terms of canon hierarchy. It's best to just take the canon statement on the fight; "The one time Master and Padawan fought as equals, with Vader using his anger and strength to counter the strokes of the more experienced and skilful Obi-Wan Kenobi."
Kenobi's more skilled, Vader's stronger, basically. But I do recall quotes stating Kenobi was hard-pressed initially, but found his feet (after he was kicked on that bridge).