Statistically, I think it would be fair to say that Holt has managed to produce year in and year out better than any other receiver in the league right now. The problem you get into when discussing who is the "best" though is that it can be difficult to compare talent just based on stats. For example,
Torry Holt has always been on a team with lots of weapons, so it's not always possible for teams to double him. On the other hand, Steve Smith plays on a team where his quarterback locks on to him and throws the ball his way more than he throws to anyone else on the team. Consequently, it's hard to compare how either would do in the other's shoes.
Then you can always get into issues about who is better at particular things or in particular situations. The best receiver in red zone situations might not be the best on third and long. The best player at getting jump balls might not be the fastest and the fastest might not be good at getting yards after the catch and so on and so on. There are enough really good receivers out there right now that it'd be tough to crown a clear cut number one. Torry certainly deserves to be in the discussion, though.