Snorlax: Zen Headbutt/Body Slam
Answers
Thanks. I had no luck with Snorlaxes since i start playing the game. I caught like 10 in the wild and all with ~50% ivs (except one with 82.2% but offensive moveset). Feeling so great now with this fatty Halloween gift. Now im ok with two great defenders (Lapras 2493cp Ice Shard/ Blizzard and this Snorlax).
It's hard to say, none of them is strictly better than the other. Both have their strengths and weaknesses. I would consider them somewhat equal.
Just like people said, Body Slam is harder to dodge for some people and because of that you could argue that it's better than Hyper Beam, but if for whatever reason you miss dodging Hyper Beam, it's over. Maybe it's raining and your screen isn't very responsive, maybe your hands are a bit swetty, maybe you get a tiny lagspike just when you need to dodge. Anything can happen.
Also, if you are used to attacking a lot of Body Slams, you shouldn't have too much trouble dodging it. One thing people also tend to overlook is that when they see the Hyper Beam animation they stop doing damage and just get ready to dodge, you are actually losing a lot of damage during that time, and you still might end up missing the dodge.
For all these reasons I would really call both moves equal and in the end it depends on who's attacking the gym.