The first app that I used is Sleep Cycle ($0.99). It has a decent interface- dimmed for night use. The display is dominated by the graph of your last night's sleep, then it has various statistics. Every night it rates your "Sleep quality", which I am a little confused about. Generally speaking, nights that it ranks higher quality are nights where I had a better night's sleep; however, it seems that it's largely a measure of time. Nights where I got more sleep (weekends) are better quality, though some nights when I get little sleep it judges it to be high quality, and some nights when I seem to have slept well it doesn't give me a very high quality. Also, because it's just the one number, it's tough to tell how to improve it- is it low because I'm tossing and turning, have sleep apnea, or just haven't slept long enough? There's no way to know.
Perhaps the best aspect of Sleep Cycle is the ability to add "Sleep Notes," which are essentially tags. You set up the tags you want to track, then before you go to sleep, you can check which ones apply. Later, you can look at the statistics and see their effect on sleep quality. I find that I sleep better on days where I worked out, better on weekends, and worse when my wife slept downstairs because of my snoring (which is since resolved- yay!). That last one is a bit counterintuitive because one would think I'd have a better night sleep without being woken up and told to flip over, but the data doesn't lie.
Unfortunately, Sleep Notes can only be entered beforehand, so you can't tag ">8 hours sleep", for instance, unless you know it before you go to sleep. And if you remember that you had caffeine yesterday but forgot to enter it- tough. You can add and delete tags whenever you want, but deleting them removes them from all entries, so once you delete it, it's gone. On a psychological note, I found it somewhat stressful and annoying to go through the list before bed because of all the gray areas- does a holiday count as a weekend, because I don't have to get up early for work? If I have to get up early on a Saturday, do I count it as a weekend or a weekday, or neither?
Sleep Cycle has tons of graphs, charting the times you went to bed, your time in bed and others, though they're not particularly convenient to get to or view. If you want to see how much sleep you've gotten in the past week, you'll have to tilt the phone on its side to access the graphs, swipe to the "time in bed" graph, then switch to the 10 days view.
Like all good tracking apps, it has an alarm that you can set to have a "wake up period"- a time before the alarm wherein if you seem to be drifting deeper into sleep, it will wake you up early so that you are more refreshed than if it woke you out of a deeper sleep. I have mixed feelings on the concept; usually when it wakes me up early I want to hit snooze.
If you have a RunKeeper account (not sure if you need the paid one or not), Sleep Cycle will sync up your sleep data to its HealthGraph system. It seems like a really neat idea but at the moment it doesn't seem like you can do much with the information, except see average over time on the RunKeeper website. They also sell a $9.99/year SleepSecure service which will sync/backup your data so that it isn't lost.
Another point worth mentioning is that Sleep Cycle seems to support iOS background app technology- when it's monitoring your sleep and you hit the home button, there is a banner at the top indicating that it's still running- not unlike the banner that appears when you're on a phone call and hit the home button. I assume this makes Sleep Cycle more robust- the OS won't close it.
If you have a phone with the M7 motion chip (iPhone 5s), then Sleep Cycle will record how many steps you took alongfghm n with the analysis, all by itself. It's nice to have but I haven't found it particularly useful.
Sleep Time (free version limited to 5 nights of data, $1.99 for full version) works pretty similarly to Sleep Cycle, with some key differences. For one, it includes 4 soundscapes (and the option to play a playlist of your own music/sounds) to help you fall asleep. You can set how long you want it to play.
The alarm is a bit harder to use, and can be confusing. It is set via a clock face, so it can be difficult to set it to the correct time. Also, you can't disable the alarm feature- you'll have to set it to a later time if you want it to record your sleep quality on weekends and holidays. You're also limited to a 12-hour clock alarm- you can set it for 7:10, and it will go off at the next 7:10, which is probably 7:10am, unless you go to bed really early. There's probably some advantage to this, since you don't have to worry about getting the am/pm wrong, but since you can't disable the alarm, you won't be able to sleep more than 12 consecutive hours.
Sleep Time's analysis is much better, however. The Sleep Lab tab has an easy-to-use display of the past week of sleep, with bar graphs indicating what time you went to sleep and woke up, as well as the stages of sleep. It's really nice and easy to use.
It doesn't have any kind of tagging, and it doesn't sync up with RunKeeper, though it does have its own (seems to be free) backup/sync service.
ComparisonHere's a side-by-side comparison of the same night recorded with both programs. They agree more than they disagree, so I can't say which one is recording a more accurate picture of the night.
Probably the main reason to choose one over the other is the tagging that Sleep Cycle lets you do. If you're recording your sleep data then chances are you want to get more out of it than just sleep quality and start/end times. Seeing how caffeine is affecting you, or any number of other things you can track, makes the process worthwhile. Additionally, the interface quirks of Sleep Time are reason enough to avoid it unless you really want the Soundscapes. RunKeeper integration is just icing on the cake. And it's cheaper.