Most techniques that are 'properly' accomplished in-camera, but can also be approximated in software, are generally better in-camera. No software filter can replicate the quality of bokeh afforded by a good-quality lens (although Photoshop's Lens Blur filter does a decent job).
Having said that, the Brenizer method is relatively time consuming, both in the field and in the computer, and requires a fast lens, so whether or not you do it 'properly' or with straightforward blurring really depends on what you're doing with it. If you're just taking a family portrait shot, you may as well 'cheat'. If you're taking a shot for your portfolio or for a professional wedding shoot, it's worth going the whole hog.