Personally I don't care about breed. Take a look at his feet if there strong you wont miss every second event with injury and his legs can stand the stress of galloping on different types of ground.
Other then that id say go for something with some miles under its belt if your new to eventing and that ISNT scared of water(hilarious how many people get eliminated at a water jump because there horse wont go near it)
Find a horse with a good bit of spunk and courage and you will go far. Remember the prettiest horse doesnt look that pretty when its unable to get around anything