This is from Smogon's analysis:
Like it says there, just slap on whatever your team has a weakness to.The last move depends on what your team has covered. Ice Punch allows Metagross to deal with Gliscor, while ThunderPunch prevents Gyarados from cutting Metagross's sweep short. Zen Headbutt can be used to take down Fighting-types such as Conkeldurr and has a 20% chance of a flinch, but is usually inferior to the other options.