High Jump Kick is pretty much by far the better option.
- Jump Kick has only slightly better accuracy and much less power
- Drain Punch is less powerful and Bulky Mega Lopunny is practically unheard of and definitely not best for Mega Lopunny
- HJK has much more power than all other moves listed and pretty decent accuracy so missing is not a huge concern
- One of the main benefits Mega Lopunny gained is the ability Scrappy. Scrappy allows it to hit Ghost types with both STABs it receives. As such, you no longer have to worry about the main drawback of HJK which is of course a switch out to a Ghost type.
Basically, the only concern with HJK is Protect or the occasional miss.
Also, Fake Out is extremely useful for Mega Lopunny. It provides STAB, priority, and essentially a completely free hit.
Here is a suggested set for Mega Lopunny:
Lopunny @ Lopunnite
EVs: 252 Atk / 4 Def / 252 Spe
- Fake Out
- High Jump Kick
- Ice Punch
Pretty self-explanatory. Ice Punch clearly for coverage.