I require an STM32 MCU with a minimum of 3 x SPI's and 2 x UART's 16 x analog input channels and 16 GPIO's what version best suits my requirement

[TDK]

There are many many chips that meet those requirements. Perhaps narrow it down to a particular family first:

https://www.st.com/en/microcontrollers-microprocessors/stm32-32-bit-arm-cortex-mcus.html

[Kote]

Thankyou for the prompt reply,

As you have suggested, there are many to choose from I seek direction as to the family/series I should investigate to determine the most suitable and cost effective solution.

[TDK]

Did you visit the page I linked? It shows comparisons between families.

[berendi]

Get the STM32CubeMX tool (I find it more usable than the online product selector), start the MCU selector.

Scroll down the left pane to the peripheral list, enter the required number of ADC channels and SPI ports. Don't bother with the UARTs there, the selection in broken, and I don't think there is a MCU with 3 SPI ports but only one UART. Select other required peripherals and parameters (e.g. memory) if you have an idea.

Click on the unit price column header in the results list, and scroll down to skip the not yet available ones.

Pick one which is available, start the project, try assigning the pins (except GPIOs). Don't forget about the programming interface (System core / SYS / Debug serial wire), and the oscillators if external ones are needed. Read the External / Internal clock source characteristics sections of the datasheet to determine if you need one (or two).