This is one of those aspects of fishing which comes down strictly to personal preference as this is whatever feels most comfortable to you while you’re holding a rod. One factor here though is that a split grip does take a bit of weight away from the rod which can make it easier to cast but only slightly.
A split grip handle also forces you to put your hands in the most optimal position which is good for those anglers who can slip into bad habits. A full grip on the other hand can be more comfortable as you have that soft covering all the way up the handle.
There’s no right or wrong way here and you’ll know in yourself how you most like to hold a rod. A there is no major differences between the two types you can just pick the one that is going to be the most comfortable for you.