Batman considers Shiva a bit better than him, and he's never defeated her without outside aid. This isn't too surprises as while Batman is both martial artist and detective, Shiva's just as focused on martial arts but without the side stuff.
Cassandra is the best, a bit better than Shiva or Batman, due mostly to her being raised on martial arts so heavily that it's more intuitive to her than anyone else. Comes from starting training at birth rather than once grown, and it took training from both Batman and Shiva to get that level.
Of course when I say 'a bit better,' it's still a relatively small amount, most people couldn't tell the difference between how well they get their butts kicked by those three and Batman's a very very tough fight for both.
Karate Kid is sort of as martial arts obsessed as Shiva, but from a thousand years in the future and with access to styles from many worlds. So it's sorta a cheat.
I'll do a top 12:
Lady Shiva and Richard Dragon
Bronze Tiger and Batman
Connor Hawke and Black Canary and Diana Prince (that is, Wonder Woman sans powers)
There's debate on these of course, and most can be slid up or down a few slots without much problem. Some of 'em I can't really decide on myself so I just put 'em at the same level