Sony NR is good and I have used it on a regular basis since 2001. It is actually particularly effective for the type of broadband noise your are wanting to remove but, as with any plug-ins of a similar nature, it works best when used in multiple passes of smaller increments (8-10dB) rather than trying to remove all the noise at once. Also, ensure that you are using Mode 2 or 3, as these are the most transparent. Personally, I use Mode 2 the most, as it provides a reasonable degree of noise reduction while still providing a natural result.
Having said that, personally I believe RX provides better results, particularly when dealing with more complex material. Once again, best results are to be had using multiple passes and smaller increments. Algorithm D in Advanced mode can give you fantastic results, but is very processor intensive and can take some time to run (Very relevant if you are on a tight deadline!).
I have used Waves X-Noise on occasion and, while it does sound quite natural, it has a tendency to "suck the air out of a recording" often leaving it sounding dull and lifeless. I believe this has something to do with the way their algorithm works with harmonics.
Another important factor to bear in mind is that all of the above are sold as bundles, so you don't only get a broadband noise reduction plug-in, but also clip, click, crackle, impulse, spectral, band, harmonic, etc, depending on the bundle you choose. Now, just because one plug-in in a bundle is great, it doesn't automatically mean that the rest will be too. So, if you are planning to get just one, try to get the one that will suit your requirements best.
I am a huge iZotope supporter and usually turn to their products first, both for NR (RX) and mastering (Ozone). However, for click and crackle removal I usually find Sony NR to be more effective and, for hum removal, Waves X-Hum. Obviously finances don't always allow but, if possible, it is very helpful to have to or three options at your disposal - much in the same way that a studio wouldn't only have one mic to record everything. Every once in a while I find that my plug-in of choice is just not providing the desired results and, under those specific circumstances, I am often able to obtain better results a competitor's plug-in.