I have an iPhone and iPad and one of my top 3 complaints is how garbage the auto correct is. It's not just auto correct, it's how you have to hit the tiny [x] on the suggestion to dismiss it. The [x] is to small, its not near the keyboard, and on some web sites, clicking but missing can have unexpected results.

I also have a bunch of incorrect spellings that I have accidentally added - I can't edit remove these though.

I've been seriously considering getting an Android and this along with not being able to change the default email client and browser are the main reasons.