Why does the Torah stress "Heim Nesi'ei ha'Matos"?
Rashi: It is with reference to the slavery in Egypt, when the these very same princes served as policemen, to force their Jewish brothers to fulfill their quota of bricks, failing which they were mercilessly beaten. They were now compensated by being chosen as leaders of their respective tribes.
And what is the Torah referring to when it writes "Heim ha'Omdim al ha'Pekudim"?
Rashi and Rashbam: It means that they stood together with Moshe and Aharon when they counted Yisrael. 1
Seforno: When they stood by their respective tribes as they were being counted, they felt that some of the members of their tribe were suspected of having sinned. 2
Targum Yonasan: They are the ones who were appointed leaders 3 in Egypt.
Seforno: And because they were the princes, they agreed between the to stand in the breach and bring Korbanos on their behalf to atone for them (See also Chizkuni).
Targum Yonasan translates Nesi'im" as 'Amarkelaya'