Are you doing backup only? Or also using for storage?
If backup only, just get a Ext HDD... easier and cheaper

If you are using as a backup & file server, then NAS more convenient.

Get the Standalone NAS if you are using it solely to keep files only. Not requiring additional new disk/space in the new future. Not requiring any other "server" services. It is also cheaper and easier to maintain.

Get a PC based NAS if you need the upgrade path in the future, or may require server services like DHCP, WAMP server, or whatever you need. More expensive, but better upgrade path.

you do not need a NAS to do RAID. You can easily get ESATA external enclosures to do the same thing without the hassle of network management.

look here some shops in Klang valley sells this

http://www.hotway.com.tw/products-raid.htm

I would suggest you get Synology. I have installed 3 units, and so far, all the units works flawlessly in SME environment, using it as a file server & backup server.

Synology is reliable.

I had also installed 2 units of the Buffalo 2 bay one.... 1 was extremely problematic.... their recovery process also a little different, since they the boot sector needs to be stored on the Disks, while the Synology already have a boot ROM.

At the end of the day, it depends on Budget vs Reliability.... you decide....

Not so much when the NAS is running, but when a disk "do" fail, how is the recovery process like?

You need to plan your backup well if the file are very important to you. Depend on NAS or RAID doesn't guarantee and 100% the data is safe.

Hardware fail, disaster and human problem is a list you need to consider.