Unfortunately there's really no cut and dry answer to your question. Some people do better on higher volume/lower frequency training, others do better on lower volume/higher frequency training. The best advice that we can give you is to experiment and find out what works best for YOU.
Just make sure that you give each program a chance to work (anything less than a couple months isn't enough time). Also, do not switch up if the program you are following is giving you the results that you're seeking, no matter how much time has passed. Switch up programs when they stop working, not when some arbitrary amount of time has passed.
Alternatively you could try keeping the same frequency that you've been doing, but switching the body part pairings up a little. For instance,
This might seem like a seemingly insignificant switch, but it means that your Tris will get worked all three days. They are involved in chest movements like bench, dips, etc..., they obviously get worked on the second day, and they are involved in shoulder pressing movements as well.
Bis will get hit at least two out of the three days (possibly even on the third day if you include leg exercises like Zercher squats and shoulder exercises like upright rows).
Along the same lines you might want to choose exercises for the other body parts that will place more stress on the Bis and Tris. For instance do a fair amount of supinated grip pulling moves for the back, I already mentioned upright rows for the shoulders, and possibly Zerchers for the legs. All of those will place secondary stress on the Bis. For Tris be sure to include pressing movements for the chest and shoulders.
Also, you didn't really mention this but diet is of huge importance. If you're not gaining weight, then chances are you're not eating enough. If you've hit a plateau, then once again the problem might be diet, not the program you're following.
Hope this helps.