For an in-game play through I would go with Lapras. Lapras has good HP to give it really good bulk. Combined with its G-max move, Max Resonance, you can survive all day. Max Resonance has 140 base power and the halves damage from Physical and Special moves. If you Dynamax near the start of middle of the Battle, and then you can do all the damage you want, and only take half damage. Also, Lapras has good moves like Surf, Ice Beam for STAB and Thunderbolt, Dragon Pulse, Psychic and Hyper Voice for coverage. So, due to Lapras' good coverage options, Very helpful Max Resonance, I believe that Lapras is a very good choice for your playthrpugh. Hope I helped!