I've used Blitz and ITG in the past, personally, I prefer the Blitz, they give off a better induction noise and look better under the bonnet. That said, the ITG is a fine filter which is the option if you want to save a few quid. As regards the Quickshick, its a Blitz SUS copy, but I'm unsure of its filtration properties. Generally speaking there's very little difference between them from a bhp gain point of view.
Worth a look if you havn't already seen this:
http://www.ftooc.org/contents/pages/project/filter.htm
Ciaran