The Geth. The Asari are a bit distant and cold, the Turians are too militaristic, the Batarians and Humans are too quick, greedy, and corrupt, the Hanar are creepy religious zealots, the Volus are too bitter, the Elcor are too conservative, the Krogans are crazy, the Vorcha are crazy, the Quarians are reactionary, biosupremacist racists, and I guess the one Drell you meet is OK, but he has this weird philosophy that he uses to excuse himself from being a murderer. "Oh, I'm just a tool, doing what I'm told. Yeeaaahh... no."
The Geth simply fight for their own survival and keep to themselves, out of not wanting to interfere with anybody's life. Compared to everyone else, they're remarkably well balanced, mentally speaking.