NAS or Mini Server - food for thought !

For a long time now I have been considering some network storage. My setup consists of a desktop machine (iMac DC) and a MacBook, which I use for a lot of surfing, downloading, posting to Geekanoids etc.

Now many NAS (Network Attached Storage) devices support the Mac platform in one way or another, but many reviews compain of performance problems, so I really wanted to avoid this. My main aim is to have somewhere central that I could store all the images I download, so that when I come to put a review together, all my files are in one central place.

It has come down to two choices, both of which have their own merits. First up is something like a Buffalo Linkstation Pro, which would give me a one box solution, I can leave it on all the time and have access to it from both my iMac and MacBook. The second option is a Mac Mini, to which I can connect one of my many existing USB or FireWire hard drives. This is a more expensive option, but performance should be better, it gives me more control and also a spare Mac to use should I need to.
I could do this with minimal expense with my current iMac, but the only thing stopping me is that I do not want to leave my iMac on 24/7.

So what do you all think, your comments are welcome.