azaran :
Depends on what you're trying to do with it. If you want something low power, the Green is going to be the way to go. If you're looking for just a general use drive and you don't care about the few watts of power then the Blue is going to out perform the Green.
The Greens have rotational speed that is variable. Its labeled as "IntelliPower". Generally, 5400 RPM speeds. Its why its able to go with lower power usage (.40watt to 3.6watt) and lower noise levels (21dBA to 22 dBA).
The Blues have a rotational speed of 7200 RPM. Its going to have faster Read/Write speeds but come at the cost of higher power usage (1.2 watts to 6.8 watts) and higher noise levels (29 dBA to 30 dBA).
Both have 64MB of cache and 2 year warranties.
No.most The WD Green that I have is 7200rpm.Most of the time it is there and sometimes to lower rpm(Quite rare).
It is not a bad option for 1TB storage.And even for O.S,if you maintained the drive well,it is great.It come close to that of the Blue Drive,but not quite the Black one.The blue one,back then was advertised for more reliability.Not quite sure,since the scenario has changed.
Nowadays,mechanical drives bearing similarities,it is quite a smart choice to opt Green.
Remember I am talking about 7200rpm WD green,its called something E.A.R.S.There are options for 5400rpm and 5800rpm greens.This 7200rpm models being most affordable,makes totally sense for storage.