I haven’t had any usage of EGR yet but from what I have seen on here(and just about everyone else would know more than me) with EGR you would use a lot less water.
Both are good for keeping the reaction cooler I think. Both can be used on their own with their own merits. With EGR you don’t have to manually dial in drips per second and remember to turn it off. You’re literally just taking some of the exhaust gas out of the tail pipe and redirecting it into your nozzle intake.
Water can be as simple or as complicated as you like. Bruce in his MGB has a water mister to add smaller droplets and also probably so he can more easily control or shut down the water supply.