So for me, the choice would be between the Black (7200rpm) and the Green (5400rpm) models. Since the Green runs cooler, it'll probably outlast a Black in the same situation, so I'd choose the Green one.

Sure, the Black is (slightly) faster. It seeks faster, which is great for a busy server. But in a home server situation, the difference will be negligible. And the cooler, lower power consumption of the Green wins.

That's my view, anyway.