Semtech led LoRa is projected as an open standard through the LoRa Alliance, but the reality is – as of now the only manufacturer of semiconductors for LoRa is Semtech and all existing modules and even gateways are strictly based on a recipe provided by Semtech to select companies. So on paper LoRa is open, but the ingredients needed to make Lora solutions are available from only Semtech and the recipe is also controlled by Semtech.
Sigfox on the other hand does not claim to be open and is on a network provider model. Sigfox has licensed out the semiconductor to third parties, but has retained the gateway side of the network. So in effect you can only get on to a Sigfox network as and when Sigfox creates a network gateway in your neighborhood. Obviously there are many limitations in this model for it to ever become a universally accepted solution for LPWAN applications.
Historically, Monopolies have been bad for innovation and so is the state of affairs with LPWAN at this time. But until a universally accepted open LPWAN technology comes up LoRaWAN and Sigfox are the options.