I recommend Mudkip because when it is fully evolved it has the highest base stat of all of the other fully evolved starters. It's speed may be low but all of it's other stats make up for this. It also has only one weakness, but at the same time it is a quad weakness.
Either way it's up to you! :)
you should start the game from the beginning.
You should definitely get Pokémon Emerald.
To get Pokemon from emerald to pearl or diamond all you have to do is put both games into the ds and start up piokemon pearl/diamond at the menu choose MIGRATE FROM EMERALD then follow the instructions by pressing yes. But remember you can't get these Pokemon back to emerald.Choose 6 Pokemon to migrate and then the Pokemon should be in pearl/diamond.Remember you can't migrate for at least 24 hours.
There should be a move deleter in Pokemon Emerald, try to find this person and you should be able to delete your moves.
you really should get emerald cause Pokemon ruby and Sapphire are separate and emerald is those 2 put together so instead of getting ruby and getting groudon just get emerald and you can get groudon and kyroge and newer Pokemon
to trade Pokemon from emerald to diamond follow these steps in order (but first you have to beat diamond and have the national pokedex.to obtain the national pokedex you have to see the 149 Pokemon of sinnoh[not including palkia.] 1.have emerald and diamond in the ds at the same time 2.have at least 6 Pokemon in the PC on emerald 3.turn on the ds and select diamond 4.at the selection screen(where you choose to continue or start a new game)choose "migrate from emerald" 5.choose "yes" for all of the questions they ask you about you migrating Pokemon 6.touch the 6 Pokemon you want to migrate(they should be in your PC) and then they will be in the pal park 7.once they are in the pal park you have to catch them note: you can only migrate once you have caught the six Pokemon and it has been 24 hours since you migrated hope i helped:)
you should get absol
easy stroomish
yes you should start over in Pokemon emerald cause you may forgot all the other rare Pokemon if you completed the game you should restart it or you will just be bored of it
emerald ruby
its your choice there are no better starter Pokemon then the rest and you will need each at different times so it doesn't matter.
not for emerald but for Pokemon silver for Gba