A Windows phone just doesn't give a good enough reward to exploit or find exploits for, it's not that there aren't vulnerabilities.
It is nice to see we've come full circle. That has been the Microsoft defense for years for Windows and everybody is quick to downplay it.
I've yet to see lag or stutter on an Android device, though I suspect that has to do more with buying crap phones than the OS
My HTC One M8 lags and stutters and I have to reboot it. Granted, not all the time, but it certainly does. You might want proof, but I'm too lazy for that, so you'll have to take it from me or ignore it. Plus, Windows pones are rumored to perform well even on low end HW, but hey, that's only what I've heard.
...and the UI looks like the garbage 8 interface.
Personal opinion. So, I really like the interface on both Windows 8.1 PRO and Windows 8.1 Phone, so there, that should balance it.