RebelTech has great prices, NGR Computers has awesome support, Prophecy has always been solid and even though I've only used Wootware once they were also very good.
+1 for prophecy. Once I got RAM that was dead and they went so far as to send me loan RAM to use while they were exchanging the faulty ones, all at no cost.
Support is very good and great with returns if you have a problem.
I've also used wootware once as they were the only ones who had any 16:10 ratio screens (a dead breed thanks to 1080p).
Service was good, can't vouch for after sales support as I didn't need any.
The majority of people here are from JHB/CPT so most of you would rather buy stuff from stores based closer to you, however NGR computers (based in Durban) have match or beat price policy which is pretty neat and they have great service too, recently had some trouble with a MSI gtx 670 power edition and the MSI agent was giving them crap, after a month of MSI messing them around and me not getting a replacement card they decided to replace me with a gigabyte windforce card at no extra cost.
used DC3 since they were just down the road from my work, but the service was pretty horrible. Then used Landmark and Prophecy for a while, but recently just make use of Wootware.
All of them are pretty prompt after proof of payment, the real difference is when you get a faulty/wrong part. So far I've found woot to have the best after sales service so highly recommend them. They also have 5 diff bank accounts, one for each of the mayor banks.