It depends on the matchup. Mewtwo does well almost all the neutrals except for FoD imo. In general I hate FoD, Green Hill Zone, and Warioware because I don't like the platform setups on those stages (although WW might not be so bad, I just have bad experiences on that stage and it's an excellent cp against Mewtwo for characters like Bowser and Falco. FoD and GHZ work against your vertical kill potential and is good for characters with a wall jump and horizontal kill power like Mario). I think Lylat is an excellent stage to cp as Mewtwo because the ledges mess up most recoveries which already serves your gimp potential well and you can cheese players with side B stage spikes.