Different people need different things from a calendar. I personally have two of them on my iPhone (in addition to Apple's built-in Calendar app). If you're looking for the right one for you, I've tested the best of them and determined the overall best of the bunch, with a handful of great others you might like for their various features.
Calendars 5 connects to your Google account and it has incredibly useful month, week, and day views. You can see everything at a glance or switch over to a daily list view if you want to focus on upcoming events. It has natural language support for quickly adding events, and you can create recurring events, set reminders, and build to-do task lists. Even rescheduling events is easy with drag-and-drop support.
Bottom-line: Calendars 5 is perfect for the organizer who prefers to see what is coming up in a full calendar view with easily identifiable events.
One more thing: It integrates with the built-in Calendar app and Reminders app, so you can take care of daily tasks and scheduling events all in one place.
Why Calendars 5 is the best
Has the best interface, fast scheduling features.
Calendars 5 covers everything I need to keep my daily, weekly, and monthly life organized. The app has a fantastic user interface that makes it possible for different people with different needs have a fantastic experience.
The Month view shows all of your events on a grid, color-coded by calendar type so you can easily see what's coming up at a glance – it's the perfect display for checking your month's schedule. Someone invited you to a party in three weeks? You can quickly glance at the Month view to see if you've already got plans.
You can also switch between daily and weekly views if you need a little more clarity into the near future. When in the daily view, you can see upcoming events relevant to the current time. The weekly view shows your events stacked together across a seven-day week.
If you prefer, you can display your daily schedule like a list, without a calendar view at all. Events are divided out by date and time, but they look more like a task list.
Speaking of tasks, you can create tasks that are incorporated into your calendar. You can even check them off when you've completed them and if you connect the built-in Reminders app, you can take care of those to-do items, as well.
As far as a straight-forward calendar app goes, Calendars 5 is the best one on the iPhone.
For Google diehards
This is Google's branded calendar app, and, as you might expect, it syncs perfectly with Google Calendar and provides detailed information from your account. It can even tie into your other Google services, like Gmail, and automatically add flight information and hotel reservations. The Schedule view features attractive illustrations based on words you have used for an event, like "flight" or "birthday". You can also switch to a one-day view, three-day view, or week view.
Bottom-line: If you are deeply integrated with all-things Google, this is the best app for your needs.
One more thing: The schedule view has pleasant, zen-like imagery. If your busy life stresses you out, Google Calendar makes it seem less crazy.
Best for today-focus
Fantastical 2 connects to the built-in Calendar app, Google, and Exchange. It also connects to the iPhone's built-in Reminders app, so you can stay on top of your to-do list. The monthly view shows a dot to let you know when you have events and also lists your daily reminders and events at the bottom half of the screen. It has an amazing natural language event creation feature. As you type, your words will drop into an event form and set the date and time. It also supports geofencing for location-based alerts.
Bottom-line: If you are the type of person that focuses on today's schedule more than you check upcoming events, Fantastical 2 is great for showing you your daily workload, while also giving you a quick glance at the month ahead.
One more thing: Fantastical 2 has a light or dark theme to compliment your mood.
Best for productivity
Informant is so much more than a calendar app. It is also a task manager, a weather tracker, a note keeper, and more. You can set up your view to see all of your scheduled events and to-do list on the same screen, and you can switch between daily, weekly, monthly, and yearly views and even treat your calendar like an agenda.
Your project and task lists stay on top of the screen, and when you've completed a task, it will be crossed out so you can easily see what you've done and what still needs to be done today. Tasks can be customized for Simple, GTD, or Franklin Covey to work with your needs.
You can set up filters that show only specific calendars that you choose; you can then switch between these calendars with just a tap. So, if you want to keep your work and home life separate, you can do so without having to go in and turn off calendars every time.
Bottom-line: If you live by your calendar and need to keep your daily tasks in view at all times, Informant is the productivity calendar for you.
One more thing: With an in-app purchase, you can subscribe to a number of useful calendars, like holidays, moon phases, weather, and more.
Follow the Sunrise
Outlook is actually an email app, not a calendar app, but you may recall that Microsoft bought Sunrise and the development team plunged into its new gig with enthusiasm. Outlook Mail now has a Sunrise-esque calendar that works pretty darn well.
It isn't a perfect Sunrise replacement, but you can see the similarities right away. You can even add some third-party apps, like Wunderlist and Evernote. There are supposed to be more apps coming soon (here's hoping that Trello gets on board).
Bottom-line: If you liked what Sunrise was all about, try Outlook for your calendar. Bonus feature: It comes with email!
One more thing: You can use Outlook with any email account, including Gmail. So don't be intimidated by the Microsoft brand.
Calendars 5 is the best
Calendars 5 is the best straight-forward calendar app for the iPhone. It has a fantastic user interface and the best looking monthly view. Plus, there are plenty of customizable features to make it versatile for different people's needs. If you are begrudgingly moving away from Sunrise, Calendars 5 will make that transition a little easier for you.