The idea of Rav Israel Salanter of learning a lot of Musar seems to make sense from the standpoint that in fact good character traits--"to be a mensch" -is the essence of Torah. However, to know what are good character traits does not seem possible without Shas. Learning Gemara in depth. So when I have a choice, I would rather learn the Avi Ezri or Tosphot which go into the depths of the Gemara. Musar seems for me to be along the lines of orientation, rather than an actual source of knowledge. [The Chazon Ish makes this exact point in his short Musar book.]
In fact, you can see, the main positive aspect of Musar is in yeshivot where it is learned as a side dish to the main thing--Gemara, Tosphot, and Rav Chaim from Brisk or the Avi Ezri.
[Though I admit that learning a lot of the Hafetz Haim about the laws of Lashon Hara would make a lot of sense.]
