Brian,
I have both the Tonewheel B4 software (by Native Instruments) and a Roland VA7, together with a Roland XV 3080 and a couple of samplers (Akai S2800 and Ensoniq ASR10); in the past I have also owned a Suzuki Hammond XK2 and a lot of older synths (Roland, Korg and Yamaha), so I think that I can speak out of personal experience. While I agree that the software option (B4) is the one which comes closest to the real thing, I have to say that it's a bit awkward for a live situation (if you want to modify the drawbars settings you have to use a mouse or another similar device and that takes time). In this kind of situation the hardware solution is much more practical; from my experience I can say that the VA7 has a lot of great sounds sampled from actual Hammond organs, with and without Leslie, percussion, distortion and so on and satisfies all my present needs for Hammond sounds, from Jimmy Smith to Procol Harum.
I remember that a few years ago Keyboard Magazine compared side by side all those Hammond "clones" and the conclusion was that the best ones were the Suzuki Hammond XK2 and the Roland VK7, with a slight edge for the latter.
Regards,
Andrea