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I would say hands down HTTP as far as the broader OEM project goes. HTTP has been around a lot longer and proved a very stable, robust and accurate way to get data into emoncms. MQTT is used between emonhub and emoncms on the emonSD and has had a pretty bumpy road to date, but most of the reliability troubles have been dealt with now, However, where the HTTP is a direct connection the MQTT is still dependent on at least one extra moving part, the broker, and there’s the emoncms MQTT input service too.

Having said that, I’m not overly experienced with using emonSEP this way so cannot comment too much on that specific use, but sending data from an emonESP using MQTT, you are not sending it direct to emoncms, you are just publishing that data to the broker and emoncms is listening in, using the same MQTT input script as used on the emonSD.

In practice you may not detect any differences or issues with either, but I bet if there is a problem, the HTTP route will be more resilient and less likely to falter.

There can be some very valid reasons to use MQTT rather than HTTP, but a flip of a coin isn’t one of them. If you do not need to specifically use MQTT, stick with HTTP. I’m sure someone is likely to point out they have had no issues with MQTT and quite possibly you might not either, but HTTP is undoubtedly the more solid of the 2 when posting to emoncms.

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