SPD3303X/X-E for one important reason, truly isolated channels without any common ground.
From what I remember, this took a while to discover because it only is a problem if CH2 and CH3 are connected in specific ways in the DUT, for example putting CH2 and CH3 in series. Mentioning this, which in many cases can be worked around, without mentioning how severely limited the third channel is on the Siglent SPD3303X (three fixed voltages, no metering, no remote voltage programming and a fixed current limit, as opposed to the fully variable remotely programmable voltage and current and metering on the DP832) is disingenuous, in my opinion.
I would say that CH3 has limitations on both the Rigol DP832 (common ground between CH2 and CH3) and Siglent SPD3303X (no metering, very limited voltage and no current adjustment), and which of the limitations affect you the least should guide the choice (other than considerations like price, service in your region and availability).