Multiple SPI, I2C, etc buses
Layout

For the PCB, the most important thing if you have many chips on the bus, is the impedance matching. If you separate the buses, it's easier, because you don't need to think (or less) about routing topology.

Frequency of reading on the chip

Using one chip by bus, you can increase the frequency of reading value on the chip. Because when a bus is running, you can use another.

If you use the DMA, it's even more important. Because while a channel is used, the DMA can sent value to another.

Bus configuration

If you have different chip with different bus configurations like:


Clock frequency
Signal phase
Signal polarity 


You don't need to re-configure the bus between two accesses.

summary

The choice depends on your project, but if you have enough free pin to separate your boss, do this.