Upgrading HTPC Storage: Internal, External or NAS?

[Morfik]

Like a lot of people on these forums I have an HTPC built around the Antec Fusion Case that's now a couple of years old. When I built it I filled both internal 3.5" bays with 1TB Samsung F1 drives which have been reliable and quiet. I'm now approaching the capacity of these drives and am not sure the best way to proceed to increase storage in a cost-effective, reliable and quiet way. I see there being three options:

1) Internal - Replace one of the internal drives with a quiet 3TB drive eg, Western Digital Caviar Green 3TB SATA 6Gb/s 64MB cost £115, but I lose 1TB of storage in the process.

2) External - Buy an external drive eg, Seagate 3TB FreeAgent GoFlex USB 3.0 3.5" Black Desktop Hard Drive - but my concern is how reliable are external drives if left on 24/7 as my HTPC is? And will they be noticably noisier than quiet internal drives? Cost ~£140

3) NAS - Add a budget NAS such as the WD My Book Live. I don't need a fully featured NAS as I'm happy to leave my HTPC to do downloading etc. However there's some reports of these being unreliable? Anyone have any experience? This is also the most expensive option: ~£170

I also intend whatever I choose to share the drive over the network. I'd be grateful of any suggestions people have of the best route to go down?

 

[R088ieS86]

Internal - 2x Samsung F4 2TB. very quiet and not a bad speed. never had any problems with them in my htpc. If you start to run out of space on them It might be worth thinking about a home media server - which I have moved to due to now exceeding 8TB of space. I wouldn't waste your money on prebuilt NAS enclosures, they are too expensive.
You could build a cheap server for the price you get them.