In my opinion not too much differnce, beside mixing ( which not realy proven yet). As long as it is balanced more or less close, the shape realy doesn't metter, that shape , which you see on the pic ( world champion in speed air modeling), of delta is done to create counter weight. Some people will talk about cranckcase volume, but it has been proven years ago, any cuts on web ( conter weight) don't make crancase volume bigger at all.
I preferd delta-it is asking less thikness of counterweight on opposite side of cranck pin area, which is realy realated to crancase volume.