Then how about the Waves IDR and the Izotope MBit+ (MegabitMax) ?
Some people said Waves IDR Type 1 sounds like POW-R 2
They may be right... although the noise-shaped dither shouldn't really have a sound -- the whole point of the psycho-acoustic shaping is that you shouldn't hear the dither noise energy! I've not compared these dithers directly, so can't offer any qualitative opinion.
However, different noise-shaped dither algorthms do put energy in different places, and it's really about finding a dither algorithm that suits the material you're working with. To illustrate the kinds of variations on offer, here is a plot of the four Prism Sound SNS dither options:
As I said, I mostly use SNS2, because it offers a lower perceived noise floor than SNS 1 or flat TPDF dither, but is relatively modest in the amount of noise shaping applied -- particularly at the high end. In contrast, the highly shaped SNS3 and SNS4 offerings, while being subjectively quieter still, can sometimes sound 'strained' and less natural to my ears... and they wack in 30dB of HF noise which can rob the headroom in very bright recordings, like close-miked brass bands!
In 99% of recordings the material's own noise floor will completely swamp any dithering subtleties and you really won't notice an audible difference between any of the noise-shaped dither algorithms on the market. The main thing is that you do apply dither when reducing the wordlength. The kind of dither is really just the flavourings of the icing on the cake!
Technical Editor, Sound On Sound