Depends can you get them from another game or will you have to get to a certain point and even then its up to you every pokemon is going to be good for something,but if it was me I would go with a Dragonite or salamence of course I would have there pre evo forms to start with.
It doesn't really matter all that much - all you really need is a solid fully evolved Pokemon (start with a basic that evolves into said Pokemon) that you are comfortable using. Try looking for something with a BST of at least 500; that's a good guideline to go by.
Internals is good, but you are going to have to grind a bit to get it's defenses up. It isn't possible to sweep everything in the game, it's going to take hits. A bulky Pokemon is usually the best choice, but Infernape is good for a quick playthrough.