Yup. I can't stand Cortana. Only works half the time. I disabled her.
Siri is the most fun to joke around with. I've asked Siri to build a snowman and marry me so many times. She refuses every time.

But as far as a useful personal assistant, Google on Android is the best. Shows me exactly what I'm interested in, even shows me information about where I am. For instance, I just looked, and it was showing that I'm in AK, which I am. Yesterday, it asked if I wanted to tag a photo I took at TSM to being located at TSM. And I can say "Okay Google" in a noisy room, and because I programmed it to recognize only my voice, it'll hear me. Although it also picks up my mom's voice as well.