I have a TTS on my Night Train, had one on my FLHTK. I currently have a PV on my CVO.
Though you'll hear differently from people, they both do the exact same thing. I have the older TTS (black) units, and they're more cumbersome to use than the PV due to the fact that you have to lug a laptop around. The PV, with its display, makes for a much easier to use tuner, and has the huge benefit of being able to see what cells you need to hit while doing a tuning run.
The TTS has a slightly higher sampling rate, and has a few features that the PV doesn't have yet, but I don't see that as a big deal to 95% of prospective buyers. Neither the PV nor the TTS have the ability to record every spark event, hence the reason you need to get multiple hits in your cells. The additional functionality simply isn't a big deal on the TTS for people who are doing a simple Stage 1 or 2.
The typical owner wants to load a base map, do a couple of tuning runs, and be done with it. It's my experience that the FM base calibrations for the PV are better than the TTS base calibrations, so that's a big plus to the PV.
I don't regret getting a PV for my new bike. It's far easier to get good tuning data than the TTS was, and I prefer WinPV to Mastertune for ease of use.