Apps that record mileage for your runs..

I also use mapmyrun. I have used both the paid and free app both are good (a few more features but don't really use them).

Any GPS will have a degree of error but you'll find a dedicated GPS like Garmin a little more accurate but I haven had an issue with mapmyrun. HRMs will not track your run unless it has GPS included. Most models of Garmins come with HRM.

I use Endomondo and it works fine. I used MapMyrun for a while and it worked pretty well most of the time, but it lost a "real" (organized) 5k I did. I understand from others' comments that this is very rare and probably just bad luck, but I switched after that. They are very comparable; both will post info here, show your route with splits and a graph so you can see pace all along the route, save history, etc. You can use more than one at the same time for a while and then drop the one you don't like. I also tried Strava but did not like it as well.

One feature I really like with Endomondo (and I think MapMyRun has, but not sure) is the count down. I put my phone in a holster to protect from sweat, accidental touches, etc. So I press the countdown button and it starts at 10 seconds. It counts the last 5 out loud and by then I have it in the holster and I know it is in there and operating before I run. I also use the feature to have it announce the splits out loud so I know if I am going too fast or slow at each mile. I have recorded about 250 miles with it over the summer.

Just to clarify about the trouble I had with MapMyRun - it did show me the info on the run on my phone when I finished the race. It failed to upload and I was in an area with spotty reception. When this happened to me with EndoMondo, it kept the data and uploaded it later. Others have told me that MapMyRun will usually do that also. What I did not like about Strava is that it was inaccurate during the run and only corrected when posting.

What do you all mean by splits?

You can choose to record your pace/time at certain intervals. Most people do mile or km splits so you know what your pace was for each. I also like the voice feedback at each mile telling me my average pace, etc. I think that's only a feature on the paid mapmyrun app.

I also lost a run once with mapmyrun but now just wait until I am in good service to hit the save.

I've just started using RunKeeper. I'm still figuring it out but so far I like it.

I LOVE RunKeeper. Its awesome! You can set it to tell you how far you've gone based on time or mileage and when you're done it shows a map of where you've been. You can sign up for different training plans too. Right now I'm doing the half marathon plan. Almost all the training plans are free too.

Another great point - RunKeeper updates to MFP for you with the time you ran and how many calories. Its so nice!

I've been using runtastic over a month now and I'm quite satisfied with it. It maps my run, tracks elevation and speed and has a voice that informs me after every km.

Or would an HRM do the same thing?

A Garmin Forerunner (they have a variety of models) will give you a combination of HRM & GPS. Depending on which model you chose it may come with their Training Center software or access to Garmin Connect (the on-line equivalent) (Timex & Suunto also have similar offerings and there may well be others but Garmin seems to dominate the market)

I pop my ANT receiver in my laptop before heading out for a run and by the time I'm done stretching my data has already been uploaded from the watch.

I use Runkeeper, which gives very good and accurate distances where I live (in the middle of nowhere) but I have heard it can be a bit flakey if you live in a city. Don't know why.

I've also tried Strava, which I like, but it doesn't link with MFP, which Runkeeper does.

I used to use Endomondo, which was super great at what it does, but stopped using it once I got my Up.
Someone says that they're pretty sure Endomondo overstates burned calories. I agree, but all those maps do so too.

I think they all overstate calories. Endomondo is giving me about 158 calories per 10:30 mile and I weigh 170. I think that is high by maybe 25% or so, comparing it to calculator at Runner's World:
http://www.runnersworld.com/tools/calories-burned-calculator
a recent run that Endomondo said was 1338 came up as only 1079 at Runner's World.

ETA - One thing it may be taking into account is elevation. I often have a variation of 150-200 feet in absolute altitude between the highest and lowest point on the run with lots of rises and drops along the way.