After evaluating the RDA5807M and the SI4703, I found out that it's hard to get good quality RDS-reception.  I only tested on a breadboard.  The air wire connections and the absence of a large enough ground plane aren't helping to get good reception quality.

The used development platform has an influence as well.  The ProTrinket 3V, powered by the FTDI has a average 5dB better RSSI than the Nucleo STM32F103.  On the Nucleo, it wasn't possible to receive four consecutive blocks without error.  The SI4703 had to be set to RDS-debug mode to get at least some RDS-info.

RDA5807M

• This chip is based on the SI4703.  The RDA5807M datasheet even contains statements that have been literally copied from the SI4703 datasheet.
• There's no error checking on the last two of the four RDS blocks.  Block 3 and block 4 contain the useful data.  The only way to "guarantee" data integrity is only passing on data that has been received twice identically.
• Reception quality is acceptable for audio, but not for RDS.  There's only one station that gives me acceptable RDS reception.
• The RDA5807M has more or less the same settings as the SI4703, but these are located at other registers.  So they're not firmware compatible.
• Very little info about the RDA5807 : 2 datasheets (in english) and two programming manuals (in chinese)
• Available on module by AliExpress

Si4703

• Extensive info available on SiLabs website
• Available on module by AliExpress
• If you need RDS, better to choose this IC instead of RDA5807M.  The RDS reception quality isn't better, but at least you'll be told what RDS-blocks are valid and which ones contain too many errors.

Si4749

• RDS only, no audio
• hard to solder QFN package
• Acceptable price : €2.30/pce at Digikey

Si4731-D60

• Used in the more recent versions of the taiwanese Sangean WR-2.
• Expensive : €13.85/pce at Digikey