Would it be advised to use Ubuntu 14.04 LTS over 12.04 LTS?

performance reasons

Performance is largely dependent on the actual application you're running. If there's specific kernel improvements in the area of performance you'd like to take advantage of you can leverage the LTS Enablement Stacks for a later kernel version and associated programs

security reasons

Given that 12.04 is an LTS edition, any security fixes in supported packages will be backported to 12.04.

In order to minimize risk and changes in your environment, I'd suggest sticking with 12.04.

When it comes to performance, lots of things have changed between 2012 and 2014 when it comes to Linux kernel, glibc, and all the other layers you meet between the kernel and your application.

If your application is truly fine-tuned and everything below it is the true bottleneck, then upgrading to 14.04 might help you. This is very unlikely, most of the time when it comes to performance the bottleneck is the application you need itself, not the underlying software/libraries/kernel.

In case you are sure your software is such a top-notch piece of diamond which absolutely can gain huge improvements in terms of performance by upgrading to the latest software, then go for it. If this is not the case, stick with 12.04 LTS.

If you have spare time / resources, just install your software to 14.04 LTS, benchmark it (and QA it to see if it works), then see if you could gain something if you upgrade.

Whatever your situation is, it never hurts if you have an idea how your software performs on some more recent piece of operating system / Linux distribution.

I think it's worthwhile to weigh in a bit with a different pragmatic sort of view rather than technical.

Since you are relying on google and community support, a year or two from now you will be more likely to find legitimate help with new packages and whatnot with 14.04 than 12.04

Though the opposite might be true right now...

Worth factoring into the equation imho