This season I am in my level cl and +1 cup. The top teams in both competitions have around the same power, but +1 cup seems easier to play. 120% teams in the 4th week must be anyhow active and spending at least time, while 100% in cup (which is seen as 120 by me) is nothing special, so I was able to crush them so far.
So from my experiences the level debate isnt really important, I even prefer +1 lvl instead my level (same power).
The only argument against it could be, that teams+1lvl can buy 99% or even scouts which, but I see it as almost irrelevant, because I am more and more convinced about the importance of white skills.