If you're into the guitar synth stuff, the GR-55 is a much better product to look at than the VG-99. The GR-55 is really fun out of the box. I'd still have to vote for the TriplePlay being the goto item for pitch to midi though. You would need a box like the iConnectMidi4+ or Kenton makes one, that will take the TriplePlay USB stick and convert it to Midi.
Tracking of pitch for the Roland line of products utilizes what amounts to a zero-line crossing counter. For a low E string, which oscillates at under 100Hz, you're looking at around 30ms for the low E to travel across the zero-crossing enough times to detect pitch. The higher the frequency of the note you are playing, the faster the Roland unit detects pitch. So, the high E string tracks faster than the low E. It can be a little off putting at times. I never really had a problem with it, but have heard of others not being able to adjust.
The TriplePlay/Axon uses a statistical method, "neural network", in their marketing. You strike the string and the TriplePlay uses what it knows to guess the string pitch from the initial pick attack. This allows the TriplePlay to guess pitch, very accurately btw, much faster than the Roland. I believe all strings can be detected in under 10ms. Maybe it is something like 13ms for the low E. Regardless, it is faster across the board and latency between strings is similar instead of having a 20ms spread.