People with green cards or citizenship are subject to the same unique worldwide citizenship-based taxation scheme that the US has. You will have to revoke your green card anyway to escape it so I would just get the citizenship since you can renounce it later with a somewhat more involved process. You can be subject to an exit tax if your 'rich enough' when you revoke your green card or citizenship. Something like $150k annual income for 5+ years or $2+ million in assets. Research it yourself, etc.