I switched years ago after my Android progressively got worse every day. Performance got slower, battery lasted shorter, and the amount of stuttering and crashing increased steadily. After about 6 months, the phone was almost unusable. This was back on Honeycomb, I think, but it left a horrible impression for my first Android phone.
I'm sure it's improved some since then, but I feel like I'd be gambling. I watch my friend's HTC One M8 take an absolute nosedive after the first year. Now, it won't even power on despite numerous attempts to save it. He switched to iPhone when the 6S came out, and he said his favorite thing about switching was "the fact that I can actually use my phone."
I guess it varies from device to device and user to user. My wife's HTC One M8 was a great phone and even after a year of usage, its still very fast. She left it because she got the iPhone 6s.
Cheers !