most important con of SRAM based FPGA:- need to be programmed on power up, each time, unless its got some other device to program it on power up automatically from some PROM or some thing.
most important pro of SRAM based FPGA:- Fast and low power programmabilty, Less space for storing config data
most important pro of Flash based FPGA:- Will retain the config data even after power down.
most important con of Flash based FPGA:- Design need to be secured, to prevent copying. Loss of chip area for allocation of Flash, Power needed to program and re program the Flash in case of EEPROM flash.