I managed three days with Headspace and just haven't picked it back up, the 10 introduction sessions seemed alright but a bit samey. I've had a look at The Mindfulness App when it went on sale for 10p and found that rather lacking, I seem to think the accent was annoying to me but it's been a while. I have Stop, breathe and think installed but haven't given that a go... I think I heard good things about it though! Want me to give it a review?
Stop, breathe and think sound interesting, try it out. I don't think you will find an app that will have something new for you every day. It is practice, and sometimes you need 15 sessions to find out how a specific technique actually works. If you happen to try headspace again and get to day 10, let me know. I have a 1-month code left.