How can I get the best ICP returns? Is it better to stake 4 years and unlock immediately, or to stake 2 years and then unlock after 2 years?
The best strategy to maximize ICP return (regardless of when you want your ICP out) is to make your dissolve delay as high as possible and then compound your returns, meaning take any ICP rewards you get and reinvest them into your staked neuron. Compounding is currently a manual activity, but the Dfinity foundation has been considering automatic compounding as an NNS app feature upgrade.
If you want to maximize liquid ICP (meaning available ICP that is not staked) then the question is more nuanced and you should check out the guide here: https://icp.guide/the-best-staking-strategy-to-maximize-liquid-icp/