I currently use FreeTrack and a DiY baseball cap -- it works fine for me (even on Win 10).
FaceTrackNOIR also worked for me (much better than for SubLtOliver evidently), but it is definitely inferior to FreeTrack, albeit easier and cheaper to try out. I did find that it wasn't as smooth, room lighting conditions have a much bigger effect, and it tended to glitch more often, so I'd only recommend it as a spare or as an inexpensive introduction to head-tracking.
I've not had any experience with OpenTrack, or any of the Arduino accelerometer types of solutions.
I've also not used the commercial version of TrackIR either.
In terms of expense, ease of use, and capability I'd say:
TrackIR: Most expensive, least effort to use, (arguably) the smoothest working, has product support, but the clip can be fragile and has a tendency to break easily
FreeTrack: Free software, requires a webcam and you need to build a cap / clip to use it (skills req'd and costs involved vary, but it's 3X cheaper (or more) than TrackIR, and pretty easy to build with a little electronics knowledge), very smooth and responsive once you get done tinkering, self supported product, and pretty reliable (depending on your building skills )
FaceTrackNOIR: Free software, requires only a webcam, cheapest of the choices, but not as smooth as either of the other two, is more twitchy and affected by room conditions.
Hope that helps.
PS> I've been using my DiY cap reliably for the past couple years now without any issues. It's worked well for me (cost was about $20-$30 USD and an afternoon of building / tinkering). In fairness, it was also the 2nd or 3rd version I'd built (the first was a headset clip based on a coat hangar -- which worked surprisingly well, and the second was my first crack at a ballcap, which worked fine, but broke often -- the current one is much better). Regarding costs, I already had ballcaps, coat-hangers and the led's, so that $20-$30 is total cost including the couple "prototypes"