Her fighting style all seem Greek based and Gladiator Style, not sure if it is specifically listed. How she is ranked as a fighter would depend on how you define it. She is more of DC's Earth's most prominent combatant, not DC's "overall" number one.
Well coming from the new 52, she is a master in Amazonian techniques. Not only that but Ares also taught her other hand to hand and sword techniques. So being the taught to fight by her mother(who was able to go toe to toe with Zeus) and by Ares(the incarnated human of war) she knows many fighting styles.
Still don't understand how Katana could be her equal thought. Diana swords skills>>>>>>>Katana's.
When people say "toe to toe" they mean in the context of all parties putting forth a serious effort, I'm going to go out on a limb here and assume Zeus wasn't going all out with Hippolyta, considering his goal seemed to be to eventually seduce her, kind of hard if Zeus completely dominated her as it would shatter their whole better than male attitude (for lack of better term).