Though I still feel little bit uncomfortable to deploy 32 arch systems on x86_64 machine.
Well, I’m not sure there’s a chip out there anymore that doesn’t support 64 bit.
So in that regard, nearly every machine would support both 32 bit and 64 bit.
When you have less RAM… something in the 512MB range, it’s a bit more cut and dry a decision… that’s a low memory situation, and at that point, using a 64 bit system may be downright wasteful, as you’ll be constantly struggling to find ways to free up RAM just to keep your services from running out of memory and dieing.
When you have 2GB of RAM, there’s a bit more to discuss
I’m sure you’ll get lots of opinions both ways, and it will ultimately come down to what your needs are.
I personally feel that, even with 2GB of RAM, that the RAM is more valuable than the architecture. Running a 32 bit system, you could serve twice as many concurrent Apache users without needing to swap. Or you could load more MySQL data into memory. And so on.
I have my own VPS server with 2GB of RAM, and I chose to install a 32 bit OS onto it, as I wanted to avoid RAM problems, and I felt that was more important than any performance increase I might see with a 64 bit OS.
But, it really comes down to your own needs. If you can, you might even consider doing some benchmarking with the web apps you want to run, putting them on both 32 bit and 64 bit systems, and seeing what sort of performance differences you run into.