Map My Run versus Strava

[Megatron]

I seem to get different information from both, the seem to vary by quite a bit - which do you rate as most accurate?

What sort of data differs? If you have a GPS enabled device with you, the mapping shouldn't be too far out as the data source will be that device. But if you're talking about calories burnt and you're not using a heart rate monitor, they'll both have their own algorithms for working out calories burnt which will be different.
My trainers link to map my run and my heart rate monitor to Garmin. I use my Garmin for the more accurate heart rate measured but the distance recorded is pretty much identical.

Thank you, that helps, it was the difference in calories that was the largest so that makes sense.

Even inside Garmin, it can differ.
If I enter a swimming session manually and say I trained for an hour, Garmin says it's 800 odd calories. However if I actually set an activity on my watch with the heart rate being picked up, I get approx half that as it's going off my actual heart rate rather than a set of calculations