Ultimately terms like "true quad core" don't really mean much in the end. It's true that AMD's architecture for multi-core processors is theoretically more efficient, but in practice Intel's design is ultimately superior. As of the introduction of the "Core" architecture Intel has really stolen AMD's thunder. It was about time really as Intel's Netburst architecture frankly sucked out loud.
Anyway at this point Intel's Core architecture is the current state-of-the-art and although AMD's Phenom CPU's are low-priced, ultimately Intel still has the price-performance crown I think. The Q6600 quad core 2.4Ghz CPU has been the "sweet spot" for price/performance on the Intel side for about a year now, but we're nearing the tail end of that timeframe I think. If I were looking at a new system now I'd personally consider waiting a bit. If you'd have bought a Q6600 6-8 months ago you would have got a really good deal for the time, considering overall performance in the market, etc. Now the Q6600 hasn't changed price much in months and is becoming less attractive IMO. On the other hand the Q6700 and other higher-end CPU's are just overpriced IMO.
Intel released the Wolfdale .45 nanometer series earlier this year, but the major advances were only with SSE4 instructions and a lower power consumption from the die shrink. Not much interesting in terms of performance and the top speed is only dual core at 3.0Ghz. That's quite fast actually, but really not *that* fast considering it's more than a year after the 2.4Ghz Core 2 "sweet spot" CPU's were available for very cheap. So in other words it's not yet a big step up from the move to .45nm.
However within a few months we should see new .45nm CPU's, more of the Penryn generation (that refers to the overall architecture generation, not the specific CPU series, e.g. Wolfdale is of the Penryn architecture generation), some with as many as 6 cores. At that point you'll either get really good deals on the previous generation (still nice performance and now cheap), or you can spend a bit more and get some of the new improvements: faster clock speeds, more cores, less power usage for a given speed, etc.
Buuuut, wait even a few months longer, to Q4 '08, and you will see the introduction of "Nehalem" on the high end. These are "only" going to be quad core at first, but they will include the return of simultaneous multi-threading (SMT, like Intel's previous hyperthreading), except that this time it's supposed to be a lot better than hyperthreading was. So you'll have 4 physical CPU cores but the possibility to execute 8 threads at once. There will also be dual sockets for these. Assuming the same clock speed as we currently have, these will outperform current generation Intel CPU's. They should also be available at even higher clock speeds, although obviously at a price premium. This will also mark the introduction of Intel's own onboard memory controllers, finally making them "true quad cores" as Moodflow put it. Again this should improve performance even further. Word in the industry is that Nehalem should be pretty awesome.
All that being said I frankly wouldn't look at a computer purchase within the next 6 months as being an all-out, high-end replacement for a current system. Everything is so cheap these days it really makes sense just to buy a workhorse for cheap, to tide you over. You can grab a quad core system with 4+GB of RAM for less than $600US in some cases. You don't need an amazing graphics card unless you're doing gaming, and even then there are some amazingly cheap, high-performance options (8800GT). So personally I'd buy now or soon, possibly waiting until the next (and last) iteration of the Penryn architecture to get the best prices, and then wait until I can see how Nehalem turns out and particularly what the price and clock speeds are like. If the price is right and clock speeds are high, I think early 2009 would be a great time to buy a new fully configured workstation with 8+GB of RAM, etc.
As for AMD, well I didn't talk about them much. I've been an AMD user for years, but there's just no getting around the fact that Intel's Core architecture has taken the crown from AMD. They're playing catch-up now. If AMD pulls something great off I'll be right back to recommending them - I'm not invested in either one. But for now I think it generally makes most sense to go Intel, and I think the Q6600 is still the "sweet spot".
- Oshyan