Out of the many that I've bought and tried, Firetask wins hands down. iPhone and iPad version plus a Mac desktop version. Does about the same thing as Things and Omnifocus, except for one crucial thing that I love... You can mark a task as "in progress" instead of just complete or not.
Do any integrate with Siri?
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I know it's expensive but I took the plunge and love omnifocus. I'm more productive and organized then ever. Siri integration is great too!