My opinion: give Latios Solar Beam and give 1 Mewtwo the extra move...beyond that I’d wait for Heatran...you didn’t mention stardust but I always start out thinking that 500k+ isn’t just a drop in the bucket.
I say Latios with Solar Beam bc I just always assume someone will have a Kyogre, can’t count on a 2nd move Groudon neutralizing that threat. Guess question would be what 2nd move to give Mewtwo...electric or ice?