Push/Pull Legs is far more popular, only big differences that I can think of is that on a common chest day you do a compound pressing moving like a bench press and a compound pulling movement like a row on a back day. The PPL separates this onto different days (so you might have more energy) where as the arnold puts these two big lifts on the same day. Ofc you can choose not to include one of these compounds and you can also add the military press as another compound movement (so dependent on your specific training). But both follow a 2 day rest after training a specific muscle

also think about how many exercises to include to target each of these muscles, generally 2-3 per muscle group, so depending on your routine, you dont want your arms/shoulders day longer in comparison