What is the best instrument for Push Notification (for Android and iOs)?

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http://stackoverflow.com – I found a few services, which are suitable for me: 1) Urban Airship http://urbanairship.com/ 2) Pushwoosh http://www.pushwoosh.com/ 3) Xtify http://xtify.com/ 4) Parse http://parse.com/ What solution do you use and why do you prefer it from others? (HowTos)