High frequency full body is best imo
Got this idea from Eric Helms who trains full body 5x a week and Jeff Nippard recently started doing the same as well. I've been doing an upper/lower split 4x a week for the longest and just switched over to full body 4x a week. I used to do the standard full body 3x a week before that, but each workout was lasting way too long.
So basically the reason it's better is because as long as weekly volume remains unchanged, the full body routine better spreads it out compared to other routines which improves set quality tremendously. Instead of doing say 8 sets for a muscle in a session done twice a week, it's better to do full body 4x a week doing only 4 sets per muscle each workout. It's still going to be 16 total weekly sets in both instances. Most of your volume becomes more effective since you'd do less junk volume because doing 4 sets for a muscle is less fatiguing than doing 8 sets for a muscle in a session. Think about it. If you're doing hard, quality sets, it doesn't take many sets for that muscle to get so fatigued that you have to start dropping reps and weight. This also means that if someone was training 6x a week doing PPL, they'd be better off doing full body 6x a week doing a few quality sets at a time for each muscle every workout.
Now some people would say, yeah but if you train full body with a high frequency, you're training the same muscles everyday and you can't do that. Well, that couldn't be further from the truth. As long as weekly volume is kept the same, you can get away with training the same muscle multiple days in a row. It's all just a matter of balancing intensity, frequency, and volume. There's even a study done on this subject called the Norweigan Frequency Project that you can check out on Menno Henselman's website right here: [url]https://mennohenselmans.com/training-frequency-3x-vs-6x/[/url]