Your initial understanding of the two products is correct, both have parametric building object capabilities. For example, both have Walls, Doors, Windows, Stairs, Railings, Slabs, Roofs, Schedules and Rooms/Spaces.
Both are geared toward Architects and architectural design and production. Both also have lots of tools for working in and managing architectural projects such as projects, levels, tags, symbols, schedules, detailing tools, keynotes, standard content, elevations and sections, etc.
Both have companion products for other disciplines like MEP and Structure (Structural is built into AutoCAD Architecture and a separate and more robust package for Revit).
Both products can be used to take a typical architectural project from start to finish (schematic design to CDs). Both products are used in firms of small, medium and large sizes on projects of all sizes.
That is a summary of how they are similar. How they differ can be summarized as follows:
AutoCAD Architecture is as its name would imply, based on an AutoCAD platform. It includes the full functionality of AutoCAD within it in addition to all the architectural tools unique to AutoCAD Architecture. Revit products are not based on AutoCAD nor do they require AutoCAD to run or AutoCAD knowledge to be used.
AutoCAD Architecture approaches projects using familiar XREF methodology. Projects are comprised of a series of related files linked together via a tool in Architecture called Project Navigator. The process is "additive" - many files "add" together to create a single project.
Revit approaches begins projects in a single integrated database file. If the project is small and only one person is working on it at a time, the project can all be stored in a single file. If multiple people need simultaneous access, the file is broken up into pieces via linked files and/or worksets. This makes Revit "subtractive" in its approach meaning that the whole is broken into pieces for coordination and collaboration. Revit manages all the pieces (coordinated copies really) and keeps all pieces synchronized.
AutoCAD Architecture's biggest strength is its familiarity and tight integration on the AutoCAD platform and the pervasive DWG file format.
Revit's biggest strength is the fully coordinated "parametric change engine" (to quote a marketing term) that means that a change in one place (view) is a simultaneous change in all views. All changes in Revit are coordinated across the entire project.
As for BIM: Building Information Modeling is a general concept rather than a specific piece of software. Many products are capable of face-lifting BIM including of course Revit and even AutoCAD Architecture despite what Autodesk says in its marketing. (This statement might get me in trouble... ) . BIM is all about creating fully coordinated, computable building design information. The concept is simply to create a full virtual simulation of the building as it will exist when completed. A BIM can be used to facilitate design, construction, procurement, pricing, life safety, ongoing maintenance, facility management, and much more. In most cases today, firms implementing BIM have only begun to scratch the surface of its potential. Revit is purpose built with BIM in mind. AutoCAD Architecture really evolved into a BIM solution candidate, but is in most cases used in some lesser capacity by the large majority of firms that use it. So in this case, Autodesk is not wrong when they say that Revit, not AutoCAD Architecture is a "true" BIM solution.
Many factors come into play when trying to decide which package to use. it is a difficult choice because both are fully capable of meeting the needs of the typical architectural firm today. Factors that are often considered are (in no particular order or priority) firm size, type of projects (firm specialties), skill level of users, cost of training and implementation, availability of skilled workforce (new hires), ongoing commitment and desire to embrace new technology, downstream values of BIM for the firm and potential to sell new services to clients, level of satisfaction or dissatisfaction with current tools and procedures, competitive edge, etc.
I have clients that use both products and I regularity get new calls for training, service and support on both. Contrary to a few of the other posts, there are no current plans announced by Autodesk to retire AutoCAD Architecture. The product is still in active development and will have a new release this year and into the foreseeable future. Revit will of course enjoy a long future as well.
Take the time to read posts on the other newsgroups out there. Carful however, as this question often sparks heated discussions/debates of the “my software can beat up your software” variety. Also look on the Autodesk website, get a demo from your local reseller and get copies of both products to try on a 30-day basis. Just realize that BOTH products require a change in traditional mindset/methods. Training is recommended and starting slowly on a smaller project is also a good idea. Commitment/buy in from management is crucial. Many folks have walked this path before you, but the one thing that both camps share in common is that after having a successful project under their belts, they rarely contemplate returning to “old” methods. Good luck!
