Well, of the two that I have used extensively, iOS and Android, I'd have to say that they both suck pretty hard. I have an iPhone for day-to-day use, which is regrettable in a number of ways but overall it's not a bad device. Aside from that though, I think that iOS is a terribly designed operating system for a number of reasons. Firstly, it looks absolutely hideous. It's simply a mess of ugly-looking icons, with a very much dysfunctional notification center that also happens to look terrible. This wouldn't be too much of an issue if you could customize it and edit the interface to your liking, as is possible with Android. Unfortunately, there really is no way of actually making your interface look any good because of the fact that you're not allowed to edit anything. This leads me into my second primary issue with iOS, which is how locked down it is. Now, this issue isn't exclusive to just Apple's iPhone, but it is very prominent here. The OS is so locked down that it doesn't even have a file browser, a basic function that should be found on a device advertising itself as a miniature computer in your pocket. That speaks volumes of the way that Apple treats it's customers, and I'd rather not get into this discussion again here, but just know that iOS is terribly restricting and that is not okay.
Now, on the other hand, even though iOS looks absolutely terrible and there is no way of fixing this due to the aforementioned restrictions, that doesn't mean that Android is necessarily that much better. Even though the Android OS is a lot more open than iOS, it still takes quite a bit of seemingly unnecessary work to actually get the results that you want. It can be difficult to actually root and flash your phone with a custom ROM, or actually use a different loader because of the way that Google and phone manufacturers have things set up. In many regards, Google isn't that much better than Apple. They carry the banner of "freedom of choice" and all of those good things, yet they still restrict, in many ways, the purchase and acquisition of applications to Google Play (which, by the way is a terribly designed interface and awful storefront), unless the user has some technical knowledge. Now, the Google vs Apple debate is something else altogether, but just know that Google is not a perfect entity when it comes to the privacy and freedom of it's customers.
In a conclusion of sorts, for day-to-day tasks both iOS and Android have their ups and their downs. In the end though, they both essentially provide the same functionality and it really won't make too much of a difference to the average user if they can still check their mail, browse Facebook, and access the web in the same ways. However, to a user who likes to think of himself as technically inclined, I don't particularly like either OS. I don't have much experience in terms of developing applications for a mobile platform, but I understand that the Android dev kit is much easier to get your hands on than the iOS kit, and it's also much easier to work with because the language it uses isn't quite as proprietary. In the end though, I don't want to say that Android is better than iOS because it still have many issues that need to be addressed before I'm comfortable with calling it a superior platform. So, they essentially are both not very good platforms.