Vefa SUCKS ASS. Their prices look good but they sell crappy components and they don't keep their promises.
The first experience I had with Vefa was when I wanted to buy a 9800 SE last year. I made 3 trips to Vefa and each time the card wasn't in stock; the 3rd time the manager said he'd phone me when the card was available. He never did, and I refuse to buy anything from Vefa.
As for Chaos, I bought my first PC there in 2002 and forget to ask for the harddrive :/ (yes, I was a n00b). When I went back they gave me the drive, no questions asked; when the harddrive failed a few months later they replaced it, again no questions asked. However, lately their service has gone downhill and of course, their prices are no longer as attractive.
Also, earlier this year I took a faulty LAN cable to Chaos. They tested it and told me it was okay, but I KNEW the cable was faulty and protested until they redid the test. Guess what - the cable WAS faulty, and my confidence in their technical skills is now zero.
Cafe Java get top marks in my books. The fan on my 9800 SE (which I bought from them) failed, and since they no longer stock the 9800 SE I was worried about getting it replaced. However, they have managed to source another fan for which I am very grateful.
As for purchasing, I prefer to buy from dealers (Rectron, Frontosa etc.). Not only are the prices better, but you get a much wider choice.