Garmin 800. There would be short segments that I might reach the low 30's and it listed my top speed as 7 or 8. Then I'd try longer segments and maintain 24+ for 2 miles and each time the times would be different - by a significant amount.

To me it felt inaccurate and I've heard lots of excuses why they are inaccurate.

Either way it was influencing my riding in a negative way, so I stopped uploading my rides there.

I have a power meter, heart rate monitor, cadence sensor and Garmin. I am happy with Garmin Connect.