You need to be a little more specific than F3 v F4, as both ranges have 'green' drives in them.
The Samsung 'green' drives are tagged 'EcoGreen'. The low rpm F3s are F3EG drives, and the performance ones are the F3 ones. The 1TB F3 is a great mix of performance and value - faster and cheaper than most of the competition, which makes them ideal for a performance array on a budget.
The same is true with the F4 range - but the only 'normal' non-green drives currently are the 320GB ones, and they are the equivalent of the Black drives (and are a great budget buy). The higher capacity F4EG drives are all green, but as the price is low also they are also often a good storage drive.