As you probably realise, it all depends on what you requirements are.
I think it's generally agreed that VSTi's are superior for actual 'sound quality' - but really that's only important if you are interested in doing
'studio-quality' recordings at home, for example.
If you are an active musician, going out-&-about to rehearsals/gigs etc, then I would go for the 'hardware' option.
The other thing I might add is this... some people seem to think that 'sound quality' is the be-all & end-all for some reason.
- but how many great/classic songs do you know that were recorded 20, 30, 40 or more years ago
that didn't have the technology available today?
Furthermore - how many folks listen to music through top-quality speakers all the time???
For most people, it's iPods, car radios, TV, or a bog-standard home hi-fi.