Latios is all well and good, but having both is better! You can find Latias at the southern island. You will of course need anohter master ball no problem, just go to lilycove department store and go to the lottery corner. Get 6 matches and you get a free master ball! you can of course catch many other pokemon like groudon using this lottery technique. It's just another way of making an experienced pokemon trainer's life, a little bit easier.