I like both. I used to hit it 5x a week, the standard m-f routine. Now I do weights 2 on 1 off and on the off day Ill hit some light cardio for 45 mins or so. Works pretty well. Every now and then Ill take a full day off, but not too often. As for your question, Id go 4 days if you are trying to add more mass or 5 day split if your shooting more for a leaner body.