Over on YouTube user Lan Party Hosting has uploaded a video showing a comparison between the RTL-SDR and SDRplay. In his tests he receives various HF and VHF/UHF signals and records their SNR values in a spreadsheet which can be downloaded here. The results show that as expected the SDRplay generally outperforms the RTL-SDR. However his results surprisingly show that the SNR of the RTL-SDR is usually better when the front end LNA of the SDRplay is not used, though we’re not sure if he took into account the difference in visual SNR that can be caused by using different bandwidths.
The video and measurements also explain when and why you should the Low IF mode on the SDRplay instead of the Zero IF mode to reduce signal imaging.