As mentioned before I am a big fan of STM32F105RB as the smallest MCU that I use unless package size is an issue. I have other preferences for LQFP48 and TSSOP20. What puzle me is a comparison between STM32F103RB and STM32F105RB on functionality and prices from AliExpress. I suspect that the reason for the low price on F105RB is because they are ditching old 32Kb Versions since the New Versions have 64Kb (Just guessing)? But, the price difference is only 0.1 USD on ST’s own sites as well. You have a similar game between STM32F103CB and STM32F303CB.
| STM32F103RB | STM32F105RB | |
| MCU | 32 bit ARM M3 | 32 bit ARM M3 |
| Frequency | 72 Mhz | 72 Mhz |
| FLASH | 128Kb Flash | 128Kb |
| SRAM | 20Kb SRAM | 32/64Kb (1) |
| Package | LFPQ64 | LFPQ64 |
| PSU | 2 – 3.6V | 2 – 3.6V |
| PVD | Yes | Yes |
| x-tal | 4 – 16 Mhz | 3-25Mhz |
| Internal x-tal | 8 Mhz | 8 Mhz |
| Power | Sleep, Stop, Standby | Sleep, Stop, Standby |
| VBAT/RTC | Yes | Yes |
| ADC | 2 x 12 bit, 16 channels | 2 x 12 bit, 16 channels |
| DAC | – | 2 x 12 bit |
| DMA | 7 channels | 12 channels |
| 5V Tolerant IO | Yes | Yes |
| SWD | Yes | Yes |
| Timers | 7 | 10 |
| I2C | 2 | 2 |
| UART | 3 | 5 |
| SPI | 2 | 3 |
| I2S | – | 2 (On SPI) |
| CAN | 1 | 2 |
| USB | 1 | 1 |
| CRC | Yes | Yes |
| Unique ID | Yes | Yes |
| Price | Ca 2.5 USD | Ca 1.6 USD |
(1) Current datasheet state 64Kb SRAM, while older datasheet state 32Kb SRAM.