I asked a similar question recently on photoshopgurus. I think that, to a certain extent, the best plugin for a particular enlargement depends on the content of the image (and possibly the look that you're going for).
The original image in the examples above is quite busy, with a lot of detail at the pixel level. For an image like this, you probably don't want to use Blow Up as it picks a few hard edges which makes it look like a painting (unless that's what you want).
I'm not sure about Photoshop's built in interpolation. It appeared to me that it didn't try to follow any edges and that the 'Preserve Details' just added a Smart Sharpen after rescaling, which doesn't really cut it for keeping sharp edges.