In early April I ordered a Nexus 5 to replace my two year old iPhone 4s. It's the first Android device I've ever owned so I've had to learn a lot of new behaviors. While doing so, I've kept a list (in Google Keep) of anything that I've found to be noticeably better or worse than iOS. Lots of my iOS-only friends have been surprised to hear about many of the differences so I'm including it here with comments added. It should also be fun to read in a few years when all of this is horribly outdated.
Better on Android / Nexus 5
- Voice interaction - I hardly used Siri on my iPhone but use the "OK Google" features all the time on my Nexus. It's easier to start using (you just say "OK Google") and it very rarely misinterprets what I say.
- Notifications list - On Android, the notifications in the top-of-screen pulldown can have action buttons on them, show rich content like images, intelligently group by app (yet stay in chronological order), and are just more useful than on iOS.
- Home screens / icons - Being able to place app icons wherever you want is great. And being able to entirely remove icons you don't want is even better. There's no need to make that "Unused" folder on Android that you stick the Stocks/Video/Compass/etc apps in. Instead, any apps you don't have represented on your screen can be found in a big Launchpad-like menu.
- There's a "+1" button when you have a timer running which just adds 60 seconds. I use this a lot, especially when grilling. :)
- Permanent buttons at the bottom of the screen for "back" and "switch apps". It's great to have a back button in such an easy to hit location (instead of iOS' top left buttons) and it works the same way in almost all apps so you don't have to learn specific behavior. And the app switcher button is so much easier to hit than double-tapping the iOS home button. I find myself using it much more often.
- Google Apps are better. Not too surprising. But since I use them a lot, this makes a big improvement to my daily usage.
Better on iOS / iPhone
- Notifications show up on the lock screen. On Android the phone will make noise or beep but you still have to tap a button to turn it on, then swipe down the top menu to see the contents. It's a real pain, especially if someone texts you while you're doing something else (video games, cooking, etc) and you can't simply glance over at your phone and see what's up.
- Home button on the front of the phone. On the Nexus the on/off button is on the side which makes it far harder to hit quickly with one hand. It also has the added benefit of helping you glance at your phone and understand which way its facing. I end up picking up my Nexus upside down all the time.
- Bottom swipe menu gives quick access to flashlight/camera/etc. On Android you can get access to some stuff from an icon in the top swipe menu, but there's no flashlight option built in.
- App quality. Looking for apps in the Play store reminds me of browsing for Windows shareware in the early 2000s. There are lots of crappy options full of ads that make it harder to find the good stuff.
- Battery percentage in the toolbar. You have to install a special Android app to get this, and even then it ends up showing on the top left, not top right. Feels awkward.
There's a lot of other random stuff I prefer on one phone or the other, but overall I am much happier being on the new setup. Of course, upgrading from two year old hardware was going to be a big improvement either way.