EEPROM is by far the slowest alternative, with write access times of around 10 ms. Access to reading is as fast as FLASH access, as well as the overhead of setting up and running an address. Since there is no automatic increment in the EEPROM address registers, each byte reading will require at least four instructions.
SRAM access is the fastest (with the exception of direct register access).
FLASH , SRAM, (Z-), SRAM, .
. AVR, LPM LDS, LD LDD.