Another Z28 CAI and PTB here, couldn't be happier with them.
Truth be told though, CAI, Rotofab, Z28, are all good choices.
There's a
link to Ted Jannetty's testing of a bunch of different CAI's over in the V8 forum, if you dig around a bit. I've just linked directlky to the spreadsheet of the results. It's on google docs, and I've got it saved in my bookmarks from back when I was researching this. It's a bit dated, but my main take away from it is, the best engineered ones perform pretty similarly to one another.
I just went with the Z28 because I'm trying to use OEM parts on this car wherever possible. Just the theme I've decided to go with. The aftermarket suppliers make some incredible parts too, and I've no aversion to them when GM hasn't given us a viable upgrade alternative for the part in question, solid sub-frame bushings as an example.