These Pokemon are incredible, yet their both different.
Clawitzer is more of an attacker (sp. atk.) rather than anything else. I really love his "Mega Launcher" ability. Since he majors in sp. attack, this ability would work best for him.
Dark Pulse, Dragon Pulse, Water Pulse, Heal Pulse, and Aura Sphere are all the moves effected by these moves - in a good way. Each of these moves are boosted by 50%, making them extremely powerful. The only bad thing about his speed and partially defense and sp. defense. So these areas are what you want to increase. Timid would be a great choice for him, but Calm/Bold works well to. Also, I recommend using a Quick Claw or anything that will increase your attacking skills.
Lapras on the other hand, has incredible HP. He does have a higher base stat total, but not by much. Lapras doesn't seem like much of an attacker nor a defender. He looks like one of these Pokemon that you have in your party, for HM's/TM's or team boosting ability - such as assisting your team with Rain Dance, Perish Song, etc.. If you choose Lapras, definitely modify him if you're making him an attacker, otherwise he's alright.
I don't know exactly how your going to use these Pokemon, but:
Clawitzer on the attacking side
Lapras on the HM/TM, assisting side
Both Pokemon are great, but for different uses. Your Choice! Hope I helped! :)