I spent about the past year using Android, but I just couldn't take it anymore. Being back on an iPhone feels like a huge relief. Why I Chose Android Last Year:

To back up a bit, I switched from an iPhone to Android last year for a few reasons:

The iPhone mail client doesn't support merged inboxes. This effectively meant that I couldn't manage my work email from my phone, since I have one Gmail "page" manage multiple email addresses. (Yes, I know you can add multiple email accounts to an iPhone. But if I did that, then my sent items wouldn't be merged.)
I wanted to be able to send SMSs online (via Google Voice). The iPhone doesn't let Google Voice override your outgoing calls' caller ID, and so doesn't support Google Voice well.
I wanted to be able to create 4G wifi hotspots. Android supports this; iPhone doesn't even support 4G.

Each of these were pretty huge value-adds of an Android for me. I knew the apps wouldn't be as good on an Android, but what was that compared with the phone being superior in terms of the most common things I do on a phone (email and SMS)?

Why I Went Back to iPhone

What I didn't expect was how frustrating the Android would be on a daily basis.

Certainly, the biggest issue was the battery life. It was terrible. My phone couldn't even last a day with pretty minimal usage. I tried everything I could think off -- re-installed the OS, upgraded to a new OS, got a new phone, tried different battery management apps, turned off 4G, etc. Nothing worked.

But even beyond the battery life, there were all sorts of little issues that made the phone feel very poorly designed and frustrating to use:

Annoying notifications. The phone would vibrate / beep to alert me that the battery was fully charged. This means that every single night -- and frequently right as I'm falling asleep -- BUZZZZZZ. I know this isn't a huge deal, but, who on earth thought this was a good feature? Poor design.
Caller ID was slow. The caller ID would sometimes take 10 seconds or so to kick-in, so I often couldn't tell who was calling. This presented a problem frequently with my building's buzzer, which rang my phone. I wouldn't realize it was the buzzer and wouldn't think to buzz someone in.
Google Voice issues. In order to send SMSs from my Google Voice number (which is the only number I wanted people to know of), I couldn't use the built-in SMS app -- only the Google Voice app. (If Google could fix the calling caller ID issue, why can't they fix SMS?)
Slow. The UI was frequently slow, non-responsive, and clunky. I hated using it.
Frequent reboots. The phone would frequently freeze. I had to reboot it every several days. I've missed many phone calls because of this.
Bloatware. The phone had a lot of pre-installed apps that you couldn't remove without rooting the phone. I'm not talking about things like Calculator that you might actually want to use -- I'm talking about golfing games and strange apps that most people would never use. It reminded me of the bloatware when you buy a new computer. (Yes, I did root the phone, but I shouldn't have had to do that.)
Poor app management. Apps were always sorted in alphabetical order. So when you installed a new app, or just wanted to find a specific one, it could be hard to find it. Yes, you can add "shortcuts," but there was no real concept of grouping or re-ordering apps the way that the iPhone allows. This is particularly problematic given all the bloatware.
GPS issues. The GPS often didn't work on Google Maps.
Navigation issues. Even when the GPS worked on Google Maps, somehow the GPS on the turn-by-turn Navigation app would rarely work. It worked at most 5% of the time.
MMS / Google Voice issues. Google Voice just dropped MMS messages. That is, if someone sent me a picture, it would just... disappear. They would think that I received it, and I would never know that there was a message. There was no error message on either side. (Of course, this isn't Android's fault, but it is Google's.) This became an even bigger issue when iPhone started supporting group SMS', which also uses the MMS protocol. Friends would send me a group message and I would never receive it.

I know, I know -- each one of these isn't a big deal. But this is just a partial list, and all these tiny little issues add up to a phone that I hated using. The only thing I really loved about Android was the mail client, but that wasn't enough to keep me.

Every time I used my Android phone it felt like a chore. And that's why I switched.