I take it you mean a choice between a brand-new current model and the new-shape model?
Pros of waiting for the new model:
You get the latest model on your drive, hot off the press.
Probably subjectively 'better' in terms of handling, space, etc.
Lower deprecation (possibly).
Cons:
You will pay very, very close to list price - no discounts except token gestures!
You will be driving a new model with possible early-production bugs
You'll act as a guinea pig for dealers who will not have a clue about fixing it at first
Honda have not given any information as yet..no prices, specs, nothing. It will be more expensive, I reckon.
Your trade-in (if you're going that route) will lose value in the meantime.
If you mean the 2002-04 vs. 2005-08 model, the facelift cars are better to drive thanks to updated rear suspension and re-geared EPS (Electric Power Steering) for better feel. I prefer the updated dashboard although the design might not be to everyone's taste (some say it's a bit 'Amstrad' hi-fi like, but I think the Jazz S kept the previous interior though). And Honda sorted the EGR valve problem by then.