Is it better to stick with Max Knuckle for the attack boost or is the Crit boost from G-Max Chi Strike better than an attack boost? I would use this Machamp for Wifi battles.
Dynamaxed Machamp is better than Gigantamaxed Machamp. In your three turns of being Dynamaxed, you can get solid Attack boosts. However, the increased critical hit chance from G-Max Chi Strike isn't necessarily guaranteed -- you can still attack without a crit.
So Max Knuckle is better, as it provided a guaranteed Attack boost each time you use it. G-Max Chi Strike is less reliable.
Hope I helped!