NEW NAS USER QNAP - Need energy efficient 1TB HARD drive

Hi there everyone. I am new to this world of QNAP and am in need of urgent advice.

I have just purchased a new QNAP TS-109 enclosure. My first ever NAS device!
I intend leaving it on 24/7. Therefore I am looking for a reliable and economical 1TB hard drive.
I have done a lot of research and came across enterprise hard drives which are meant to be designed for 24/7 use. However they cost approxiamtely double the price!
Also as I have a TS-109 its only a single Bay enclosure hence I will not be using RAID.

The hard drives that I have seen are:

1) Samsung F2 ecogreen;from ebuyer @ £56.99

http://www.ebuyer.com/product/164282

2) Western Digital 1TB Hard Drive SATAII 32MB Cache - OEM Caviar Green from ebuyer @ £57.85

http://www.ebuyer.com/product/150245/show_product_reviews?offset=10&review_type=both&review_order_by=RUF

3) Samsung HD103SJ Spinpoint F3 1TB Hard Drive SATAII 7200rpm 32MB Cache @ £56.90

http://www.ebuyer.com/product/173804

I'm tempted to go for the F3 however I do not know if it energy efficient.

Also this is only my own research. The purpose of this post was to recieve suggestions. Therefore please feel free to suggest others. (Please)

Thanks for your time an effort for reading my post. It will be a pleasure if you can advise me!