. . . to really challenge more established alternatives such as Pano2VR or Flashificator + Flash Panorama Player.
What keeps you away from using Pano2VR or others instead of APT?
I have a pano2VR license, purchased long before APT existed, and also use that program. It's very good for putting single panos on-line as Flash, and I like the patch tool. However I'm too lazy to make the effort to get to grips with the some 'eccentric' and less-than-intuitive Skin Editor to learn how to link panos, create thumbnails, maps, and so on , but I admire the results produced by those who have made the effort and I can see that they can produce results that could not be produced with the current version of APT without additional hand coding.
As for Flashificator (FFC) + Flash Panorama Player (FPP) ; The Russian FPP author seems to be more reclusive than Greta Garbo ever was, and only communicates in occasional cryptic utterances communicated via a third-party. There's even been some uncertainty as to whether he's still developing the product. I can't see that FPP offers anything that krpano doesn't, and krpano uniquely offers a multi-resolution capability. Flashificator, the GUI front-end for FPP, is the brain child of a splendidly eccentric Icelander who lives in Lima, Peru. He is very communicative and supportive of his users but the future of his product is of course wholly dependent on what happens with FPP and there appears to be be no functional channel of communication between the developer of FPP and the developer of Flashficator. There are no trial versions of either Flash Panorama Player or Flashificator - so no chance to try before you buy, although neither is very expensive.
I use APT because of its exceptional ease of use for simple tours, because of krpano's unique multi-resolution capabilities, because I'd like to contribute ideas for APT's further development, and because I like Kolor products and believe that ultimately APP/APG + APT-krpano can evolve to become the undisputed 'best of breed'.