Considering how limited, unrealistic, and flat wrong the tactics or strategies employed by military geniuses in fiction tend to be, I'd say the only way to evaluate them would be 'whose backstory actually makes sense for the title of best general?', the alternative basically being to try to decide which author understood strategy best and which character they used as a proxy to discuss it, in which case RJ has a better claim than most, and I can't think of any actual generals who have written scifi fantasy, though I think I'd like to read them if they exist.

Such being the case, Benedict wins out, he's a millenia old near-demigod and spends tons of time watching battles then watching their alternate realities with minor changes, he's commanded forces big and small in places from the normal to the surreal, I'd say as major characters where descriptions are given, he probably deserves to have the title, after that Cauthon's claim is pretty solid, as opposed to Ender for instance, since Mat has the memories of a bunch of generals, thus vast experience. In the symbolic sense of things, benedict actually launched a succesful attack on the Gates of Hell in book 5 of amber, which is pretty impressive