There is, in my view, only a single correct answer. And this is based on over 10 years of building servers and RACs using h/w bought from various vendors, putting these together, installing the o/s, and getting the driver stack to work.
And there is ALWAYS an issue. Without exception. Ranging from a driver/operating system/hardware failure under stress testing, to drivers not loading correctly (requiring manual lsmod and mobprobe and custom rules), to issues like where is the Subnet Manager running and where should it be running.
And sometimes there are multiple issues.
Sometimes the problem is so nefarious it cannot be isolated. So you log the error with vendor 1 and vendor 2. Only to have vendor 1 saying it is not their problem, with vendor 2 saying vendor 1's s/w (which you have configured as per vendor 1's installation guide) is incorrectly configured.
There is a simple solution. It is relatively cheap. It comes with a fully certified h/w and s/w stack, pre-installed. With a single vendor being responsible for the entire stack. With integrated ready-to-use storage. Including SSD. Where you wheel the solution in, plug in a cable, use an admin tool to configure the network, and is up and running with a database ready to use in a very short time. Where you do not have RDS stress test failures. Or soft CPU lockups in the kernel. Or kernel panics. Or ASM failing to start due to some obscure ORA-600 error. Or a myriad of other potential issues.
It is called Oracle Database Appliance.
Only an idiot, who never had to put together RACs manually, would argue otherwise. (and of course I am referring to those idiots in management and strategy that expects you to magically build a robust and working RAC by putting together different pieces of h/w and s/w from different vendors and simply make it work in just a couple of days)
Is my prejudice showing?
I shall second to what Billy said. There is just one thing that I would add that though ODA is a part of the Oracle's engineered system's family but it doesn't come with the Exadata's Cell software. If you are looking forward to take a benefit of that (Smart Scan, HCC etc.) , you probably can spend some extra money can get Exadata(1/8th option) . Again, would depend on how much you are planning to spend. If money is a concern, going for ODA would be a much better option instead of reading and reviewing multiple spec sheets from multiple vendors and spending a lot of time putting it all together.
Just to add to Aman's comments.
If you need a smallish db server solution (e.g. 12 cores licensed for Oracle Enterprise Edition with Partitioning Option), you can use the remaining 36 cores to configure a JBoss VM for your Open Source app layer, an Apache VM for your web server needs, and so on.
As I understand from my discussion with Oracle last week, the additional cores and Oracle VM are paid for - and does not need RDBMS licensing as you are not using these for driving a database. Which enables you to add (non-db) VMs to the appliance at no additional costs.
I think you have to evaluate several aspects, such as quality, performance, support, as well as your technical abilities and budget. This means you will probably first have to make your decision on software and what OS you want to use, or can use, considering your budget and available technical support. And only then decide on a suitable hardware platform.
The Itanium CPU was designed for servers, while Intel Xeon was more or less a requirement for Microsoft and other 3rd party software and hardware relying on legacy x86 CISC code. As far as I know, the Intel/AMD x64 technology is still providing a solution for x86 with only a 64-bit extension in order to deal with the demand for more than 4GB of RAM and 2 TB disk space. The Itanium CPU however was designed for true 64-bit server solutions and to my knowledge is more powerful for parallel processing as it provides more 64-bit registers compared to Intel Xeon. Unfortunately, many vendors have dropped support for Itanium in favor of the much cheaper x64 (x86_64). (I think there was even a law suit that Oracle lost in regard to dropping support for the Itanium platform not too long ago.)
Personally I would never recommend to run Oracle database products on anything other than a very popular Unix or Enterprise Linux. If you have to use MS-Windows, and only MS-Windows, then finding a solution for MS-SQL server, which is a complete different world, might be more suitable for your technical and IT political environment.
I guess there is only little doubt that a vendor who makes the hardware and the OS can provide the best guarantee to avoid hardware compatibility issues or be able to address problems as quickly as possible. So for instance, if you use AIX, Solaris or HPUX, which only run on certified hardware, you will more likely have less hardware compatibility issues than running for instance Linux. However, I would not put too much weight on such argumentation anymore since acceptance, certification and support for Enterprise Linux, such as SUSE, RHEL and sometimes OL (with UEK kernel) has been increasing.
Among Linux, AIX, HPUX and Solaris, I think Solaris provides the most admin friendly tools. If you are looking for a modern Unix based OS, which supports pretty much every state of the art technology available, than I think Linux, and Oracle Linux in particular, is the winner. Oracle Linux when compared to other flavors of Enterprise Linux provides dtrace (Sun) and ksplice support, for instance. Support for commercial Unix solutions may generally be more effective when you require technical support for hardware and software debugging, or patches, but that's also a question of support personnel and business culture.
Taking the above into consideration, I have no doubt that Intel Xeon and Oracle Linux is currently the most economic or most efficient solution in terms of licensing, relative performance and support costs for the foreseeable future. However, Intel Xeon based servers still use a lot of PC technology. If you are looking for an absolute top notch solution, you will probably have to raise your budget by 10 times, and Solaris and Exadata might be best choice for running an Oracle database, considering also that Oracle acquired SUN. However, I would question whether the extra mile is really worth the money and rather recommend Oracle Linux and HP Xeon servers, but it really depends on your demand and requirements, budget and your available support resources.
Anyway, these were just some thoughts. Since I can only guess your technical background and do not know your budget, or real technical demand or requirements, no real advice can or should be given.
We'd probably have a better idea of your existing load if you told us about the app and users, and why you think RAC is an appropriate answer.
There is quite a discontinuity between SE and EE, especially on price with RAC. RAC will emphasize any problems with your app, and SE does not allow you to simply add a performance pack to see what is going wrong. If you crunch the numbers, you may find that discontinuity larger than the hardware costs. Do you have EE now?
You may also have found the core price multiplier silliness. Cost efficiency for cores is a strange metric, easily blown away by inefficient apps and random marketing decisions.