Alexander the Great probably tops the list of actually referenced battles he was the commander of with a handful of great battles, numerous sieges, and quite a few other battles which we only have fragmentary evidence about how large/important they were such as vs the Sycthians.
Keep in mind that a lot of the "battles" that al-Walid is credited as winning are little more than skirmishes that have been inflated to be "battles" by people with a vested interest in showing his greatness and superiority.
I would say Napoleon is the likely choice. Almost every engagement he was victorious in was a pitched battle - he fought only two sieges in his life - and all of them involved at least ten thousand men on one side or the other. He apparently fought around 60 pitched battles and won almost all of them, losing only four or five (mostly towards the end of his career).
Mongol history isn't my thing, but note the following quote from (admittedly) the wikipedia article about Subutai: 'He directed more than 20 campaigns in which he conquered 32 nations and won 65 pitched battles, during which he conquered or overran more territory than any other commander in history.'
Alex without question. For how many years did he lead from the very front fighting every mile of the way? Undefeated? Say what you will--there was only one and there will only ever be one Alexander the Great.
It would be good if users with a strong knowledge of Arab and Mongol history could weigh in on how many of those battles can be regarded as being more like skirmishes, although Kirialax does makes a good point: at what point is a skirmish a battle?