I've been using Things across platforms for years and love it. But I need something that will hit my calendar.
I found Planner Plus and Opus Domini recently
I was all set to buy Planner Plus, but their most recent update (this week!) changed the tabs to the bottom and added a lot of colors. It looked more like a real planner before they did that. I believe there are also issues with unfinished tasks forwarding to the next day, but I could be wrong about that. I did email them about my disappointment over the new format, and they said they'd take it under consideration (other reviewers noted the same issue). Response was quick.
Then I went to Opus, which was a little less expensive. I downloaded both the free apps on the Mac and iPad. The free versions won't sync to each other. Unfortunately both iPad and Mac version need the most recent OS - iOS 7 and Mavericks. I'm on iOS 6 and ML. I've emailed them asking if I can purchase the old versions and haven't heard back yet.
I like these because they allow me to add tasks and notes, which saves me from sticky note hell. I use Noteability for meetings, but there is no way to put a todo list in it with and be able to check items off as they are completed, and I really need that. Both programs above will allow that.
Things would be perfect if it only had a calendar.
Another app I downloaded was LifeTopix. I find it intriguing but a little confusing. It will accept a ton of info across every aspect of your life. I tend to use it to put some health info in, and notes because those show up on its calendar. Not sure if they will sync to the OS calendar, but an event you add into the LifeTopix calendar will.