There must be 10,000 threads on this here but here is my take.
Split pros-quieter, more control over the arrow, I shoot moving targets better, I can shoot longer targets easier with less hold over.
Split cons-can't really find any since I started as a boy in the 50s. It's a natural thing for me.
3 under pros-arrow closer to eye. Some feel they can hit close objects better, people just entering archery find it easier to master at first.
3 under cons-noisier bow, less control over arrow especially on moving targets, short point on distance which is a consideration if you shoot a lot of 3-D or roving with longer than hunting distances taken.