Either Eelektross, zapdos, articuno, giratina. Eelektross has NO weaknesses and neither does any of it's evolutionary relatives
It's durable, cool-looking, and has no weaknesses since electric is weak to only ground and it has levitate which make ground not effect.
Spiritomb and Sableye used to have no weaknesses, but 6th gen screwed that up with the addition of fairy type, which does 2x damage against dark-type... :c
Gyarados. Cause he is beast!!! Plus, I don't know why, there was a convosation about Pokemon in sb1, and I joined in, the subject? Which Pokemon would you eat? Of course I chose gyarados.
Eeveee that little adorable ball of fluff. And like I said before, Magikarp cuz he is a beast. Much better than Gyarados ;)
Your mum, it's x4 effective to all Pokemon; it's a 6th gen Pokemon and it is super super super super rare.