Which is better of thees CPUs

Cortex A7 and Cortex A9 belong to 32-bit ARMv7 architecture.

Cortex A53 belongs to 64-bit ARMv8 architecture (next generation).

If you want only best performance choose Cortex A53.

But overall performance of the system depends on different features like who manufactures the main processor, how many peripherals embedded in System-on-Chip (SoC), what kind of Operating System is installed and how it uses all features of the SoC.

Cortex A7 and Cortex A9 belong to 32-bit ARMv7 architecture.

Cortex A53 belongs to 64-bit ARMv8 architecture (next generation).

If you want only best performance choose Cortex A53.

But overall performance of the system depends on different features like who manufactures the main processor, how many peripherals embedded in System-on-Chip (SoC), what kind of Operating System is installed and how it uses all features of the SoC.