If you just started your survival world, skeletons would be very hard to kill as their health points are 20x10 and are deadly in Hard mode, but in easy, they are like Stormtroopers (If you didn't get the Star Wars reference, stormtroopers have crappy aiming). Zombies would be very easy to kill and you can easily kill one in a one-to-one hand-to-hand combat. But if you have no tools, you would need to be patient to kill one as it takes some time.