Hi @Anonymous
It really depends what you will be using it for, both can do the same thing if you really want them too.
Revit is an extremely powerful Scheduling tool. It links brilliantly between familes, parameters and schedules, the possibillites are really unlimited in this area. Also, being a much more mainstream product, it fits alot nicer into the implementation of the BIM cycle etc. and the support from Autodesk is always going to be great.
ArchiCad is easy to work with like sketch up, and the graphics are great. I can't comment too much on the 'annotation and 2D side of archiCad but i can with Revit, and its brilliant for annotating, especially in the architectural field.
As far as Collaboration goes, Revit is a no brainer, it can be used with a big host of programs with no issues. However exporting in ArchiCad has to be an IFC File to be able to be opened in anything else, the annoying part of this is you loose alot of information and model elements when you export which can be a bit of a pain. It is purely a design and visual program, and its good at that. Revit can be used for that, it can really be set up for anything depending on the user/company of course.
At the end of the day everyone has there opinions, and they are both faster/slower than each other in separate areas. Its like the PC vs. Mac debate. They both do things differently but they both get the job done. I'd suggest getting a trail version and having a play, and watch advance tutorials to see the power and possibilites!
Thanks, hope it some what helps. Let me know if you have any other questions 