A closer lookIt is notable that the Rigol is a more matured product. The Rigol does have some more options buried in the menu screens the Siglent is missing. Though these are usually no important options and Siglent might add them to later firmware versions.
Speed: With larger spans the Rigol often scans the frequency span quicker than the Siglent, however with more narrow spans and/or? narrower bandwidth, the Siglent ofter is quicker. There was not time to setup and fill a detailed table to compare the speed.
As there was no time for a detailed look and comparison of both devices. I often only went through some menus and made screen shots. They may help you as additional information if you want to decide between both devices. I always used the same signal and used the same setting on both devices.
Oh, regarding screen shots: creating screen shots on the Rigol is pretty annoying. Not only that they take ages, after pressing “save” the screen is completely filled with the file menu where you have to enter a file name. But only after pressing “OK” the screen closes and then the current screen (which has been –slowly– updated in the background) is being saved. The problem: it might take you easily 30 seconds to enter a file name and the screen being saved is not the one of the moment when you pressed “save”.
It then takes the Rigol 10 seconds to create a BMP shot and 23 seconds for a PNG shot.
The Siglent it more convenient: it shows a small box with an automatically created file name (set up of the current date and time e.g. “SSA_160617181838” which can be changed of course) inside the still-alive screen data screen. Not before pressing ENTER the then current screen (which you can always see and which is updated in regular speed) will be saved. The Siglent then needs only approx. 1 second for saving the screen shot. However, the Siglent only allows to save BMP, there is no JPG or PNG option (yet?).For the following screen shots I always set up both units to the same settings. Even if the Siglent would allow up to 2.1 GHz, I always used the same frequency span as the Rigol (0-1.5 Ghz or lower depending on the signal) to allow an easier comparison.
As Rigol screenshots usually are smaller due their lower resolution, I resized them to the same horizontal size as the Siglent shots.
Screen shots:All shots without any connection to the input.
1) Siglent at start up(up to 2.1 Ghz) - note that the Siglent has 20dB attenuator on as standard (Auto)
2) Rigol at start up - Rigol has 10 dB attenuator as standard (Auto)
Siglent is more flat than Rigol.
3) Siglent with pre amplifier on
4) Rigol with pre amplifier on
Note: Siglent does not allow ref level of -10 with preamp on. For this we are showing the difference with a reference level of -20dB (thus you need to add another -10dB to the Siglent values if you want to compare them with the Rigol). The next two pictures are showing noise level with identical settings.
5) Siglent noise floor with 300 Khz, 100Khz, 30Khz
6) Rigol noise floor with 300 Khz, 100Khz, 30Khz
Edit: Check out also Thomas screenshot https://www.eevblog.com/forum/testgear/comparison-rigol-dsa815-tg-with-siglent-ssa3021x-spectrum-analyzer/msg965865/#msg965865. On his DSA815 device the noise level is lower. Still the Siglent is better, but not that much as shown on my screen shot.