Rashi: It is better than to join with Anavim and be Shefal Ru'ach [than to divide spoils with the proud]. R. Yonah - from their company, one learns from the ways of humility. Shefal is a noun, like Yekar - "Yitenu Yekar l'Valeihen" (Esther 1:20). We find "bi'Shfal Kol ha'Tachanah" (Koheles 12:4).

Malbim: Shefal Ru'ach is the extreme opposite Anavah, which is in the middle between pride and lowliness. An Anav senses his honor, just he chooses to be Anav. Shefal Ru'ach, the images of his heart lower him, to the point that he does not feel at all when people disgrace him. In all Midos, the middle is good. Regarding pride, Chazal warned 'be very much Shefal Ru'ach' (Avos 4:4). It is good to go to the extreme. However, he should not be genuine Shefal Ru'ach who does not sense. Rather, he should be "Shefal Ru'ach Es Anavim" - the lowliness is due to Anavah, via choice of the Sechel based on Chachmah and its laws. Since Govah Ru'ach is prone to become Gevah Lev and stumble and break, it is good to be "Shefal Ru'ach Es Anavim" - the ultimate lowliness. Then he will not stumble, and all the more so he will not break.

R. Yonah: [Acquiring Shiflus Ru'ach from the humble is better] than gaining spoils and Metzi'os with the haughty.

Malbim: Even though it seems to him that he divides spoils with them and profits greatly, suddenly he will be broken and lowered. The end of humility is honor - "v'Lifnei Chavod Anavah" (15:33).