Based on the facts, venusaur is the weakest, so squirtle would be the best because charizard is the best starter besides swampert.
you would have a advantage if you have swampert if you dont like swampert get any of the types i wrote ground,rock or water types
well both of the Pokemon the leaders have, its a double battle, know psychic, and swampert is water/ground so psychic would do some serious damage, i would suggest getting a couple of other Pokemon instead and training them up to around 35s, 40s, or you can get your swampert up to around lvl 50 and then make sure it knows some good moves and then try versing the gym, i would suggest at least 5 or 6 revives and some hyper potions... good luck!
because it makes you catch that certain pokemon, and it is a title and picture for the cover or the title, say if it was a blastoise it would be something like "Pokemon Master Blastoise"
The 6 Pokemon I would recommend would be Blaziken, Swampert, Sceptile, Gardivore, Aggron and Salmence so that you have an equally balanced team.
Blastoise, Pidgeot, and Nidoqueen are very mediocre. If you want those 3 particular types, go with Swampert or Empoleon for a Water-type. For a Flying, I suggest Dragonite or something powerful like that. I wouldn't use a Poison-type since they don't really have good coverage, but a good Poison would be Drapion or Muk. As for the other 3, evolve them, and they will be extreme.
Well I would get a.... Shiftry lev 100 Swampert lev 100 Salamence lev 100 If you want the abilities of poke moves go to www.Psypoke.com
A good team would be: Salamence,Swampert,Walrein,Metagross,Manectric,Pelliper. have fun :)
If you picked Swampert, your rival would have a treecko. Other than that, I don't think there are outside the Battle Frontier.
Blastoise...obviously
i would use a arcanine because they seedy and powerful
well it kinda depends on the level and type but i would say if every Pokemon u had were level 100 i think either mewtwo or Blastoise